SGI Freeware 2002 November/SGI Freeware 2002 November - Disc 2.iso/dist/fw_gnuplot.idb/usr/freeware/doc/gnuplot/gnuplot.doc.z/gnuplot.doc

Text File | 2002-01-08 | 269KB | 6,670 lines

C RCS $Id: gnuplot.doc,v 1.20.2.3 1999/10/27 10:10:16 lhecking Exp $
C 3 December 1998
C Copyright (C) 1986 - 1993, 1998   Thomas Williams, Colin Kelley
C
^ <h2> An Interactive Plotting Program </h2><p>
^ <h2>  Thomas Williams & Colin Kelley</h2><p>
^ <h2>   Version 3.7 organized by: David Denholm </h2><p>
^ <h2>Major contributors (alphabetic order):</h2>
^<ul><h3>
^<li>  Hans-Bernhard Broeker
^<li>  John Campbell
^<li>  Robert Cunningham
^<li>  David Denholm
^<li>  Gershon Elber
^<li>  Roger Fearick
^<li>  Carsten Grammes
^<li>  Lucas Hart
^<li>  Lars Hecking
^<li>  Thomas Koenig
^<li>  David Kotz
^<li>  Ed Kubaitis
^<li>  Russell Lang
^<li>  Alexander Lehmann
^<li>  Alexander Mai
^<li>  Carsten Steger
^<li>  Tom Tkacik
^<li>  Jos Van der Woude
^<li>  James R. Van Zandt
^<li>  Alex Woo
^</h3></ul> <p>
^<h2>  Copyright (C) 1986 - 1993, 1998   Thomas Williams, Colin Kelley<p>
^   Mailing list for comments: [e-mail] <p>
^   Mailing list for bug reports: [e-mail]<p>
^</h2><p>
^<h3> This manual was prepared by Dick Crawford</h3><p>
^<h3> 3 December 1998</h3><p>
^<hr>
1 gnuplot
2 Copyright
?copyright
?license
       Copyright (C) 1986 - 1993, 1998   Thomas Williams, Colin Kelley

 Permission to use, copy, and distribute this software and its
 documentation for any purpose with or without fee is hereby granted,
 provided that the above copyright notice appear in all copies and
 that both that copyright notice and this permission notice appear
 in supporting documentation.

 Permission to modify the software is granted, but not the right to
 distribute the complete modified source code.  Modifications are to
 be distributed as patches to the released version.  Permission to
 distribute binaries produced by compiling modified sources is granted,
 provided you
   1. distribute the corresponding source modifications from the
    released version in the form of a patch file along with the binaries,
   2. add special version identification to distinguish your version
    in addition to the base release version number,
   3. provide your name and address as the primary contact for the
    support of your modified version, and
   4. retain our contact information in regard to use of the base
    software.
 Permission to distribute the released version of the source code along
 with corresponding source modifications in the form of a patch file is
 granted with same provisions 2 through 4 for binary distributions.

 This software is provided "as is" without express or implied warranty
 to the extent permitted by applicable law.


       AUTHORS

       Original Software:
          Thomas Williams,  Colin Kelley.

       Gnuplot 2.0 additions:
          Russell Lang, Dave Kotz, John Campbell.

       Gnuplot 3.0 additions:
          Gershon Elber and many others.
2 Introduction
?introduction
?
 `gnuplot` is a command-driven interactive function and data plotting program.
 It is case sensitive (commands and function names written in lowercase are
 not the same as those written in CAPS).  All command names may be abbreviated
 as long as the abbreviation is not ambiguous.  Any number of commands may
 appear on a line (with the exception that `load` or `call` must be the final
 command), separated by semicolons (;).  Strings are indicated with quotes.
 They may be either single or double quotation marks, e.g.,

       load "filename"
       cd 'dir'

 although there are some subtle differences (see `syntax` for more details).

 Any command-line arguments are assumed to be names of files containing
 `gnuplot` commands, with the exception of standard X11 arguments, which are
 processed first.  Each file is loaded with the `load` command, in the order
 specified.  `gnuplot` exits after the last file is processed.  When no load
 files are named, `gnuplot` enters into an interactive mode.  The special
 filename "-" is used to denote standard input.  See "help batch/interactive"
 for more details.

 Many `gnuplot` commands have multiple options.  These options must appear in
 the proper order, although unwanted ones may be omitted in most cases.  Thus
 if the entire command is "command a b c", then "command a c" will probably
 work, but "command c a" will fail.

 Commands may extend over several input lines by ending each line but the last
 with a backslash (\).  The backslash must be the _last_ character on each
 line.  The effect is as if the backslash and newline were not there.  That
 is, no white space is implied, nor is a comment terminated.  Therefore,
 commenting out a continued line comments out the entire command (see
 `comment`).  But note that if an error occurs somewhere on a multi-line
 command, the parser may not be able to locate precisely where the error is
 and in that case will not necessarily point to the correct line.

 In this document, curly braces ({}) denote optional arguments and a vertical
 bar (|) separates mutually exclusive choices.  `gnuplot` keywords or `help`
 topics are indicated by backquotes or `boldface` (where available).  Angle
 brackets (<>) are used to mark replaceable tokens.  In many cases, a default
 value of the token will be taken for optional arguments if the token is
 omitted, but these cases are not always denoted with braces around the angle
 brackets.

 For on-line help on any topic, type `help` followed by the name of the topic
 or just `help` or `?` to get a menu of available topics.

 The new `gnuplot` user should begin by reading about `plotting` (if on-line,
 type `help plotting`).
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/simple.html"> Simple Plots Demo </a>
2 Seeking-assistance
?seeking-assistance
 There is a mailing list for `gnuplot` users.  Note, however, that the
 newsgroup
       comp.graphics.apps.gnuplot
 is identical to the mailing list (they both carry the same set of messages).
 We prefer that you read the messages through the newsgroup rather than
 subscribing to the mailing list.  Administrative requests should be sent to
       [e-mail]
 Send a message with the body (not the subject) consisting of the single word
 "help" (without the quotes) for more details.

 The address for mailing to list members is:
       [e-mail]

 Bug reports and code contributions should be mailed to:
       [e-mail]

 The list of those interested in beta-test versions is:
       [e-mail]

 There is also a World Wide Web page with up-to-date information, including
 known bugs:
^ <a href="http://www.cs.dartmouth.edu/gnuplot_info.html">
       http://www.cs.dartmouth.edu/gnuplot_info.html
^ </a>

 Before seeking help, please check the
^ <a href="http://www.ucc.ie/gnuplot/gnuplot-faq.html">
 FAQ (Frequently Asked Questions) list.
^ </a>
 If you do not have a copy of the FAQ, you may request a copy by email from
 the Majordomo address above, ftp a copy from
       ftp://ftp.ucc.ie/pub/gnuplot/faq,
       ftp://ftp.gnuplot.vt.edu/pub/gnuplot/faq,
 or see the WWW `gnuplot` page.

 When posting a question, please include full details of the version of
 `gnuplot`, the machine, and operating system you are using.  A _small_ script
 demonstrating the problem may be useful.  Function plots are preferable to
 datafile plots.  If email-ing to info-gnuplot, please state whether or not
 you are subscribed to the list, so that users who use news will know to email
 a reply to you.  There is a form for such postings on the WWW site.
2 What's New in version 3.7
?new-features
 Gnuplot version 3.7 contains many new features.  This section gives a partial
 list and links to the new items in no particular order.

 1. `fit f(x) 'file' via` uses the Marquardt-Levenberg method to fit data.
 (This is only slightly different from the `gnufit` patch available for 3.5.)

 2. Greatly expanded `using` command.  See `plot using`.

 3. `set timefmt` allows for the use of dates as input and output for time
 series plots.  See `Time/Date data` and
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/timedat.html">
 timedat.dem.
^ </a>

 4. Multiline labels and font selection in some drivers.

 5. Minor (unlabeled) tics.  See `set mxtics`.

 6. `key` options for moving the key box in the page (and even outside of the
 plot), putting a title on it and a box around it, and more.  See `set key`.

 7. Multiplots on a single logical page with `set multiplot`.

 8. Enhanced `postscript` driver with super/subscripts and font changes.
 (This was a separate driver (`enhpost`) that was available as a patch for
 3.5.)

 9. Second axes:  use the top and right axes independently of the bottom and
 left, both for plotting and labels.  See `plot`.

 10. Special datafile names `'-'` and `""`.  See `plot special-filenames`.

 11. Additional coordinate systems for labels and arrows.  See `coordinates`.

 12. `set size` can try to plot with a specified aspect ratio.

 13. `set missing` now treats missing data correctly.

 14. The `call` command: `load` with arguments.

 15. More flexible `range` commands with `reverse` and `writeback` keywords.

 16. `set encoding` for multi-lingual encoding.

 17. New `x11` driver with persistent and multiple windows.

 18. New plotting styles: `xerrorbars`, `histeps`, `financebars` and more.
 See `set style`.

 19. New tic label formats, including `"%l %L"` which uses the mantissa and
 exponents to a given base for labels.  See `set format`.

 20. New drivers, including `cgm` for inclusion into MS-Office applications
 and `gif` for serving plots to the WEB.

 21. Smoothing and spline-fitting options for `plot`.  See `plot smooth`.

 22. `set margin` and `set origin` give much better control over where a
 graph appears on the page.

 23. `set border` now controls each border individually.

 24. The new commands `if` and `reread` allow command loops.

 25. Point styles and sizes, line types and widths can be specified on the
 `plot` command.  Line types and widths can also be specified for grids,
 borders, tics and arrows.  See `plot with`.  Furthermore these types may be
 combined and stored for further use.  See `set linestyle`.

 26. Text (labels, tic labels, and the time stamp) can be written vertically
 by those terminals capable of doing so.
2 Batch/Interactive Operation
?batch/interactive
 `gnuplot` may be executed in either batch or interactive modes, and the two
 may even be mixed together on many systems.

 Any command-line arguments are assumed to be names of files containing
 `gnuplot` commands (with the exception of standard X11 arguments, which are
 processed first).  Each file is loaded with the `load` command, in the order
 specified.  `gnuplot` exits after the last file is processed.  When no load
 files are named, `gnuplot` enters into an interactive mode.  The special
 filename "-" is used to denote standard input.

 Both the `exit` and `quit` commands terminate the current command file and
 `load` the next one, until all have been processed.

 Examples:

 To launch an interactive session:
       gnuplot

 To launch a batch session using two command files "input1" and "input2":
       gnuplot input1 input2

 To launch an interactive session after an initialization file "header" and
 followed by another command file "trailer":
       gnuplot header - trailer
2 Command-line-editing
?line-editing
?editing
?history
?command-line-editing
 Command-line editing is supported by the Unix, Atari, VMS, MS-DOS and OS/2
 versions of `gnuplot`.  Also, a history mechanism allows previous commands to
 be edited and re-executed.  After the command line has been edited, a newline
 or carriage return will enter the entire line without regard to where the
 cursor is positioned.

 (The readline function in `gnuplot` is not the same as the readline used in
 GNU Bash and GNU Emacs.  If the GNU version is desired, it may be selected
 instead of the `gnuplot` version at compile time.)


 The editing commands are as follows:

@start table - first is interactive cleartext form
       `Line-editing`:

       ^B    moves back a single character.
       ^F    moves forward a single character.
       ^A    moves to the beginning of the line.
       ^E    moves to the end of the line.
       ^H    and DEL delete the previous character.
       ^D    deletes the current character.
       ^K    deletes from current position to the end of line.
       ^L,^R redraws line in case it gets trashed.
       ^U    deletes the entire line.
       ^W    deletes the last word.

       `History`:

       ^P    moves back through history.
       ^N    moves forward through history.
#\begin{tabular}{|cl|} \hline
#\multicolumn{2}{|c|}{Command-line Editing Commands} \\ \hline \hline
#Character & Function \\ \hline
# & \multicolumn{1}{|c|}{Line Editing}\\ \cline{2-2}
#\verb~^B~ & move back a single character.\\
#\verb~^F~ & move forward a single character.\\
#\verb~^A~ & move to the beginning of the line.\\
#\verb~^E~ & move to the end of the line.\\
#\verb~^H, DEL~ & delete the previous character.\\
#\verb~^D~ & delete the current character.\\
#\verb~^K~ & delete from current position to the end of line.\\
#\verb~^L, ^R~ & redraw line in case it gets trashed.\\
#\verb~^U~ & delete the entire line. \\
#\verb~^W~ & delete from the current word to the end of line. \\ \hline
# & \multicolumn{1}{|c|}{History} \\ \cline{2-2}
#\verb~^P~ & move back through history.\\
#\verb~^N~ & move forward through history.\\
%c l .
%Character@Function
%_
%@Line Editing
%^B@move back a single character.
%^F@move forward a single character.
%^A@move to the beginning of the line.
%^E@move to the end of the line.
%^H, DEL@delete the previous character.
%^D@delete the current character.
%^K@delete from current position to the end of line.
%^L, ^R@redraw line in case it gets trashed.
%^U@delete the entire line.
%^W@delete from the current word to the end of line.
%_
%@History
%^P@move back through history.
%^N@move forward through history.
@end table

 On the IBM PC, the use of a TSR program such as DOSEDIT or CED may be desired
 for line editing.  The default makefile assumes that this is the case;  by
 default `gnuplot` will be compiled with no line-editing capability.  If you
 want to use `gnuplot`'s line editing, set READLINE in the makefile and add
 readline.obj to the link file.  The following arrow keys may be used on the
 IBM PC and Atari versions if readline is used:

@start table - first is interactive cleartext form
       Left  Arrow      - same as ^B.
       Right Arrow      - same as ^F.
       Ctrl Left  Arrow - same as ^A.
       Ctrl Right Arrow - same as ^E.
       Up    Arrow      - same as ^P.
       Down  Arrow      - same as ^N.
#\begin{tabular}{|cl|} \hline
#Arrow key  & Function \\ \hline
#Left       & same as \verb~^B~. \\
#Right      & same as \verb~^F~. \\
#Ctrl Left  & same as \verb~^A~. \\
#Ctrl Right & same as \verb~^E~. \\
#Up         & same as \verb~^P~. \\
#Down       & same as \verb~^N~. \\
%c l .
%Arrow key@Function
%_
%Left Arrow@same as ^B.
%Right Arrow@same as ^F.
%Ctrl Left Arrow@same as ^A.
%Ctrl Right Arrow@same as ^E.
%Up Arrow@same as ^P.
%Down Arrow@same as ^N.
%_
@end table

 The Atari version of readline defines some additional key aliases:

@start table - first is interactive cleartext form
       Undo            - same as ^L.
       Home            - same as ^A.
       Ctrl Home       - same as ^E.
       Esc             - same as ^U.
       Help            - `help` plus return.
       Ctrl Help       - `help `.
#\begin{tabular}{|cl|} \hline
#Arrow key & Function \\ \hline
#Undo      & same as \verb~^L~. \\
#Home      & same as \verb~^A~. \\
#Ctrl Home & same as \verb~^E~. \\
#Esc       & same as \verb~^U~. \\
#Help      & `{\bf help}' plus return. \\
#Ctrl Help & `{\bf help }'. \\
%c l .
%Arrow key@Function
%_
%Undo@same as ^L.
%Home@same as ^A.
%Ctrl Home@same as ^E.
%Esc@same as ^U.
%Help@help plus return.
%Ctrl Help@help .
%_
@end table
2 Comments
?comments
 Comments are supported as follows: a `#` may appear in most places in a line
 and `gnuplot` will ignore the rest of the line.  It will not have this effect
 inside quotes, inside numbers (including complex numbers), inside command
 substitutions, etc.  In short, it works anywhere it makes sense to work.
2 Coordinates
?coordinates
 The commands `set arrow`, `set key`, and `set label` allow you to draw
 something at an arbitrary position on the graph.  This position is specified
 by the syntax:

       {<system>} <x>, {<system>} <y> {,{<system>} <z>}

 Each <system> can either be `first`, `second`, `graph` or `screen`.

 `first` places the x, y, or z coordinate in the system defined by the left
 and bottom axes; `second` places it in the system defined by the second axes
 (top and right); `graph` specifies the area within the axes---0,0 is bottom
 left and 1,1 is top right (for splot, 0,0,0 is bottom left of plotting area;
 use negative z to get to the base---see `set ticslevel`); and `screen`
 specifies the screen area (the entire area---not just the portion selected by
 `set size`), with 0,0 at bottom left and 1,1 at top right.

 If the coordinate system for x is not specified, `first` is used.  If the
 system for y is not specified, the one used for x is adopted.

 If one (or more) axis is timeseries, the appropriate coordinate should
 be given as a quoted time string according to the `timefmt` format string.
 See `set xdata` and `set timefmt`.  `gnuplot` will also accept an integer
 expression, which will be interpreted as seconds from 1 January 2000.
2 Environment
?environment
 A number of shell environment variables are understood by `gnuplot`.  None of
 these are required, but may be useful.

 If GNUTERM is defined, it is used as the name of the terminal type to be
 used.  This overrides any terminal type sensed by `gnuplot` on start-up, but
 is itself overridden by the .gnuplot (or equivalent) start-up file (see
 `start-up`) and, of course, by later explicit changes.

 On Unix, AmigaOS, AtariTOS, MS-DOS and OS/2, GNUHELP may be defined to be the
 pathname of the HELP file (gnuplot.gih).

 On VMS, the logical name GNUPLOT$HELP should be defined as the name of the
 help library for `gnuplot`.  The `gnuplot` help can be put inside any system
 help library, allowing access to help from both within and outside `gnuplot`
 if desired.

 On Unix, HOME is used as the name of a directory to search for a .gnuplot
 file if none is found in the current directory.  On AmigaOS, AtariTOS,
 MS-DOS and OS/2, gnuplot is used.  On VMS, SYS$LOGIN: is used. See `help
 start-up`.

 On Unix, PAGER is used as an output filter for help messages.

 On Unix, AtariTOS and AmigaOS, SHELL is used for the `shell` command.  On
 MS-DOS and OS/2, COMSPEC is used for the `shell` command.

 On MS-DOS, if the BGI or Watcom interface is used, PCTRM is used to tell
 the maximum resolution supported by your monitor by setting it to
 S<max. horizontal resolution>. E.g. if your monitor's maximum resolution is
 800x600, then use:
       set PCTRM=S800
 If PCTRM is not set, standard VGA is used.

 FIT_SCRIPT may be used to specify a `gnuplot` command to be executed when a
 fit is interrupted---see `fit`.  FIT_LOG specifies the filename of the
 logfile maintained by fit.
2 Expressions
?expressions
 In general, any mathematical expression accepted by C, FORTRAN, Pascal, or
 BASIC is valid.  The precedence of these operators is determined by the
 specifications of the C programming language.  White space (spaces and tabs)
 is ignored inside expressions.

 Complex constants are expressed as {<real>,<imag>}, where <real> and <imag>
 must be numerical constants.  For example, {3,2} represents 3 + 2i; {0,1}
 represents 'i' itself.  The curly braces are explicitly required here.

 Note that gnuplot uses both "real" and "integer" arithmetic, like FORTRAN and
 C.  Integers are entered as "1", "-10", etc; reals as "1.0", "-10.0", "1e1",
 3.5e-1, etc.  The most important difference between the two forms is in
 division: division of integers truncates: 5/2 = 2; division of reals does
 not: 5.0/2.0 = 2.5.  In mixed expressions, integers are "promoted" to reals
 before evaluation: 5/2e0 = 2.5.  The result of division of a negative integer
 by a positive one may vary among compilers.  Try a test like "print -5/2" to
 determine if your system chooses -2 or -3 as the answer.

 The integer expression "1/0" may be used to generate an "undefined" flag,
 which causes a point to ignored; the `ternary` operator gives an example.

 The real and imaginary parts of complex expressions are always real, whatever
 the form in which they are entered: in {3,2} the "3" and "2" are reals, not
 integers.
3 Functions
?expressions functions
?functions
 The functions in `gnuplot` are the same as the corresponding functions in
 the Unix math library, except that all functions accept integer, real, and
 complex arguments, unless otherwise noted.

 For those functions that accept or return angles that may be given in either
 degrees or radians (sin(x), cos(x), tan(x), asin(x), acos(x), atan(x),
 atan2(x) and arg(z)), the unit may be selected by `set angles`, which
 defaults to radians.

@start table
#\begin{tabular}{|ccl|} \hline
#\multicolumn{3}{|c|}{Math library functions} \\ \hline \hline
#Function & Arguments & Returns \\ \hline
%c c l .
%Function@Arguments@Returns
%_
4 abs
?expressions functions abs
?functions abs
?abs
#abs(x) & any  &  absolute value of $x$, $|x|$; same type \\
#abs(x) & complex &  length of $x$, $\sqrt{{\mbox{real}(x)^{2} +
#\mbox{imag}(x)^{2}}}$ \\
%abs(x)@any@absolute value of $x$, $|x|$; same type
%abs(x)@complex@length of $x$, $sqrt{roman real (x) sup 2 + roman imag (x) sup 2}$
 The `abs(x)` function returns the absolute value of its argument.  The
 returned value is of the same type as the argument.

 For complex arguments, abs(x) is defined as the length of x in the complex
 plane [i.e.,  sqrt(real(x)**2 + imag(x)**2) ].
4 acos
?expressions functions acos
?functions acos
?acos
#acos(x) & any  & $\cos^{-1} x$ (inverse cosine) \\
%acos(x)@any@$cos sup -1 x$ (inverse cosine)
 The `acos(x)` function returns the arc cosine (inverse cosine) of its
 argument.  `acos` returns its argument in radians or degrees, as selected by
 `set angles`.
4 acosh
?expressions functions acosh
?functions acosh
?acosh
#acosh(x) & any  & $\cosh^{-1} x$ (inverse hyperbolic cosine) in radians \\
%acosh(x)@any@$cosh sup -1 x$ (inverse hyperbolic cosine) in radians
 The `acosh(x)` function returns the inverse hyperbolic cosine of its argument
 in radians.
4 arg
?expressions functions arg
?functions arg
?arg
#arg(x) & complex & the phase of $x$ \\
%arg(x)@complex@the phase of $x$
 The `arg(x)` function returns the phase of a complex number in radians or
 degrees, as selected by `set angles`.
4 asin
?expressions functions asin
?functions asin
?asin
#asin(x) & any  & $\sin^{-1} x$ (inverse sin) \\
%asin(x)@any@$sin sup -1 x$ (inverse sin)
 The `asin(x)` function returns the arc sin (inverse sin) of its argument.
 `asin` returns its argument in radians or degrees, as selected by `set
 angles`.
4 asinh
?expressions functions asinh
?functions asinh
?asinh
#asinh(x) & any  & $\sinh^{-1} x$ (inverse hyperbolic sin) in radians \\
%asinh(x)@any@$sinh sup -1 x$ (inverse hyperbolic sin) in radians
 The `asinh(x)` function returns the inverse hyperbolic sin of its argument in
 radians.
4 atan
?expressions functions atan
?functions atan
?atan
#atan(x) & any  & $\tan^{-1} x$ (inverse tangent) \\
%atan(x)@any@$tan sup -1 x$ (inverse tangent)
 The `atan(x)` function returns the arc tangent (inverse tangent) of its
 argument.  `atan` returns its argument in radians or degrees, as selected by
 `set angles`.
4 atan2
?expressions functions atan2
?functions atan2
?atan2
#atan2(y,x) & int or real & $\tan^{-1} (y/x)$ (inverse tangent) \\
%atan2(y,x)@int or real@$tan sup -1 (y/x)$ (inverse tangent)
 The `atan2(y,x)` function returns the arc tangent (inverse tangent) of the
 ratio of the real parts of its arguments.  `atan2` returns its argument in
 radians or degrees, as selected by `set angles`, in the correct quadrant.
4 atanh
?expressions functions atanh
?functions atanh
?atanh
#atanh(x) & any  & $\tanh^{-1} x$ (inverse hyperbolic tangent) in radians \\
%atanh(x)@any@$tanh sup -1 x$ (inverse hyperbolic tangent) in radians
 The `atanh(x)` function returns the inverse hyperbolic tangent of its
 argument in radians.
4 besj0
?expressions functions besj0
?functions besj0
?besj0
#besj0(x) & int or real &  $j_{0}$ Bessel function of $x$, in radians \\
%besj0(x)@int or real@$j sub 0$ Bessel function of $x$, in radians
 The `besj0(x)` function returns the j0th Bessel function of its argument.
 `besj0` expects its argument to be in radians.
4 besj1
?expressions functions besj1
?functions besj1
?besj1
#besj1(x) & int or real & $j_{1}$ Bessel function of $x$, in radians \\
%besj1(x)@int or real@$j sub 1$ Bessel function of $x$, in radians
 The `besj1(x)` function returns the j1st Bessel function of its argument.
 `besj1` expects its argument to be in radians.
4 besy0
?expressions functions besy0
?functions besy0
?besy0
#besy0(x) & int or real & $y_{0}$ Bessel function of $x$, in radians \\
%besy0(x)@int or real@$y sub 0$ Bessel function of $x$, in radians
 The `besy0` function returns the y0th Bessel function of its argument.
 `besy0` expects its argument to be in radians.
4 besy1
?expressions functions besy1
?functions besy1
?besy1
#besy1(x) & int or real & $y_{1}$ Bessel function of $x$, in radians \\
%besy1(x)@int or real@$y sub 1$ Bessel function of $x$, in radians
 The `besy1(x)` function returns the y1st Bessel function of its argument.
 `besy1` expects its argument to be in radians.
4 ceil
?expressions functions ceil
?functions ceil
?ceil
#ceil(x) & any & $\lceil x \rceil$, smallest integer not less than $x$
#(real part) \\
%ceil(x)@any@$left ceiling x right ceiling$, smallest integer not less than $x$ (real part)
 The `ceil(x)` function returns the smallest integer that is not less than its
 argument.  For complex numbers, `ceil` returns the smallest integer not less
 than the real part of its argument.
4 cos
?expressions functions cos
?functions cos
?cos
#cos(x) & any & $\cos x$, cosine of $x$ \\
%cos(x)@radians@$cos~x$, cosine of $x$
 The `cos(x)` function returns the cosine of its argument.  `cos` accepts its
 argument in radians or degrees, as selected by `set angles`.
4 cosh
?expressions functions cosh
?functions cosh
?cosh
#cosh(x) & any & $\cosh x$, hyperbolic cosine of $x$ in radians \\
%cosh(x)@any@$cosh~x$, hyperbolic cosine of $x$ in radians
 The `cosh(x)` function returns the hyperbolic cosine of its argument.  `cosh`
 expects its argument to be in radians.
4 erf
?expressions functions erf
?functions erf
?erf
#erf(x) & any & $\mbox{erf}(\mbox{real}(x))$,  error function of real($x$) \\
%erf(x)@any@$erf ( roman real (x))$, error function of real ($x$)
 The `erf(x)` function returns the error function of the real part of its
 argument.  If the argument is a complex value, the imaginary component is
 ignored.
4 erfc
?expressions functions erfc
?functions erfc
?erfc
#erfc(x) & any & $\mbox{erfc}(\mbox{real}(x))$,  1.0 - error function of real($x$) \\
%erfc(x)@any@$erfc ( roman real (x))$, 1.0 - error function of real ($x$)
 The `erfc(x)` function returns 1.0 - the error function of the real part of
 its argument.  If the argument is a complex value, the imaginary component is
 ignored.
4 exp
?expressions functions exp
?functions exp
?exp
#exp(x) & any & $e^{x}$,  exponential function of $x$ \\
%exp(x)@any@$e sup x$, exponential function of $x$
 The `exp(x)` function returns the exponential function of its argument (`e`
 raised to the power of its argument).  On some implementations (notably
 suns), exp(-x) returns undefined for very large x.  A user-defined function
 like safe(x) = x<-100 ? 0 : exp(x) might prove useful in these cases.
4 floor
?expressions functions floor
?functions floor
?floor
#floor(x) & any & $\lfloor x \rfloor$,  largest integer not greater
#than $x$ (real part) \\
%floor(x)@any@$left floor x right floor$, largest integer not greater than $x$ (real part)
 The `floor(x)` function returns the largest integer not greater than its
 argument.  For complex numbers, `floor` returns the largest integer not
 greater than the real part of its argument.
4 gamma
?expressions functions gamma
?functions gamma
?gamma
#gamma(x) & any & $\mbox{gamma}(\mbox{real}(x))$,  gamma function of real($x$) \\
%gamma(x)@any@$GAMMA ( roman real (x))$, gamma function of real ($x$)
 The `gamma(x)` function returns the gamma function of the real part of its
 argument.  For integer n, gamma(n+1) = n!.  If the argument is a complex
 value, the imaginary component is ignored.
4 ibeta
?expressions functions ibeta
?functions ibeta
?ibeta
#ibeta(p,q,x) & any & $\mbox{ibeta}(\mbox{real}(p,q,x))$,  ibeta function of real($p$,$q$,$x$) \\
%ibeta(p,q,x)@any@$ibeta ( roman real (p,q,x))$, ibeta function of real ($p$,$q$,$x$)
 The `ibeta(p,q,x)` function returns the incomplete beta function of the real
 parts of its arguments. p, q > 0 and x in [0:1].  If the arguments are
 complex, the imaginary components are ignored.
4 inverf
?expressions functions inverf
?functions inverf
?inverf
#inverf(x) & any &  inverse error function of real($x$)  \\
%inverf(x)@any@inverse error function real($x$)
 The `inverf(x)` function returns the inverse error function of the real part
 of its argument.
4 igamma
?expressions functions igamma
?functions igamma
?igamma
#igamma(a,x) & any & $\mbox{igamma}(\mbox{real}(a,x))$,  igamma function of real($a$,$x$) \\
%igamma(a,x)@any@$igamma ( roman real (a,x))$, igamma function of real ($a$,$x$)
 The `igamma(a,x)` function returns the incomplete gamma function of the real
 parts of its arguments.  a > 0 and x >= 0.  If the arguments are complex,
 the imaginary components are ignored.
4 imag
?expressions functions imag
?functions imag
?imag
#imag(x) & complex &  imaginary part of $x$ as a real number \\
%imag(x)@complex@imaginary part of $x$ as a real number
 The `imag(x)` function returns the imaginary part of its argument as a real
 number.
4 invnorm
?expressions functions invnorm
?functions invnorm
?invnorm
#invnorm(x) & any &  inverse normal distribution function of real($x$)  \\
%invnorm(x)@any@inverse normal distribution function real($x$)
 The `invnorm(x)` function returns the inverse normal distribution function of
 the real part of its argument.
4 int
?expressions functions int
?functions int
?int
#int(x) & real &  integer part of $x$, truncated toward zero \\
%int(x)@real@integer part of $x$, truncated toward zero
 The `int(x)` function returns the integer part of its argument, truncated
 toward zero.
4 lgamma
?expressions functions lgamma
?functions lgamma
?lgamma
#lgamma(x) & any & $\mbox{lgamma}(\mbox{real}(x))$,  lgamma function of real($x$) \\
%lgamma(x)@any@$lgamma ( roman real (x))$, lgamma function of real ($x$)
 The `lgamma(x)` function returns the natural logarithm of the gamma function
 of the real part of its argument.  If the argument is a complex value, the
 imaginary component is ignored.
4 log
?expressions functions log
?functions log
?log
#log(x) & any & $\log_{e} x$,  natural logarithm (base $e$) of $x$ \\
%log(x)@any@$ln~x$, natural logarithm (base $e$) of $x$
 The `log(x)` function returns the natural logarithm (base `e`) of its
 argument.
4 log10
?expressions functions log10
?functions log10
?log10
#log10(x) & any & $\log_{10} x$,  logarithm (base $10$) of $x$ \\
%log10(x)@any@${log sub 10}~x$, logarithm (base $10$) of $x$
 The `log10(x)` function returns the logarithm (base 10) of its argument.
4 norm
?expressions functions norm
?functions norm
?norm
#norm(x) & any & normal distribution (Gaussian) function of real($x$) \\
%norm(x)@any@$norm(x)$, normal distribution function of real($x$)
 The `norm(x)` function returns the normal distribution function (or Gaussian)
 of the real part of its argument.
4 rand
?expressions functions rand
?functions rand
?rand
#rand(x) & any & $\mbox{rand}(\mbox{real}(x))$,  pseudo random number generator \\
%rand(x)@any@$rand ( roman real (x))$, pseudo random number generator
 The `rand(x)` function returns a pseudo random number in the interval [0:1]
 using the real part of its argument as a seed.  If seed < 0, the sequence
 is (re)initialized.  If the argument is a complex value, the imaginary
 component is ignored.
4 real
?expressions functions real
?functions real
?real
#real(x) & any &  real part of $x$ \\
%real(x)@any@real part of $x$
 The `real(x)` function returns the real part of its argument.
4 sgn
?expressions functions sgn
?functions sgn
?sgn
#sgn(x) & any & 1 if $x>0$, -1 if $x<0$, 0 if $x=0$. imag($x$) ignored \\
%sgn(x)@any@1 if $x > 0$, -1 if $x < 0$, 0 if $x = 0$. $roman imag (x)$ ignored
 The `sgn(x)` function returns 1 if its argument is positive, -1 if its
 argument is negative, and 0 if its argument is 0.  If the argument is a
 complex value, the imaginary component is ignored.
4 sin
?expressions functions sin
?functions sin
?sin
#sin(x) & any & $\sin x$, sine of $x$ \\
%sin(x)@any@$sin~x$, sine of $x$
 The `sin(x)` function returns the sine of its argument.  `sin` expects its
 argument to be in radians or degrees, as selected by `set angles`.
4 sinh
?expressions functions sinh
?functions sinh
?sinh
#sinh(x) & any & $\sinh x$, hyperbolic sine $x$ in radians \\
%sinh(x)@any@$sinh~x$, hyperbolic sine $x$ in radians
 The `sinh(x)` function returns the hyperbolic sine of its argument.  `sinh`
 expects its argument to be in radians.
4 sqrt
?expressions functions sqrt
?functions sqrt
?sqrt
#sqrt(x) & any & $\sqrt{x}$,  square root of $x$ \\
%sqrt(x)@any@$sqrt x $, square root of $x$
 The `sqrt(x)` function returns the square root of its argument.
4 tan
?expressions functions tan
?functions tan
?tan
#tan(x) & any & $\tan x$,  tangent of $x$ \\
%tan(x)@any@$tan~x$, tangent of $x$
 The `tan(x)` function returns the tangent of its argument.  `tan` expects
 its argument to be in radians or degrees, as selected by `set angles`.
4 tanh
?expressions functions tanh
?functions tanh
?tanh
#tanh(x) & any & $\tanh x$, hyperbolic tangent of $x$ in radians\\
%tanh(x)@any@$tanh~x$, hyperbolic tangent of $x$ in radians
 The `tanh(x)` function returns the hyperbolic tangent of its argument.  `tanh`
 expects its argument to be in radians.
@end table

 A few additional functions are also available.

@start table
#\begin{tabular}{|ccl|} \hline
#\multicolumn{3}{|c|}{other {\bf gnuplot} functions} \\ \hline \hline
#Function & Arguments & Returns \\ \hline
%c c l .
%Function@Arguments@Returns
%_
4 column
?expressions functions column
?functions column
?column
#column(x) & int & column $x$ during datafile manipulation. \\
%column(x)@int@ column $x$ during datafile manipulation.
 `column(x)` may be used only in expressions as part of `using` manipulations
 to fits or datafile plots.  See `plot datafile using`.
4 tm_hour
?expressions tm_hour
?functions tm_hour
#tm\_hour(x) & int & the hour \\
%tm_hour(x)@int@the hour
 The `tm_hour` function interprets its argument as a time, in seconds from
 1 Jan 2000.  It returns the hour (an integer in the range 0--23) as a real.
4 tm_mday
?expressions tm_mday
?functions tm_mday
#tm\_mday(x) & int & the day of the month \\
%tm_mday(x)@int@the day of the month
 The `tm_mday` function interprets its argument as a time, in seconds from
 1 Jan 2000.  It returns the day of the month (an integer in the range 1--31)
 as a real.
4 tm_min
?expressions tm_min
?functions tm_min
#tm\_min(x) & int & the minute \\
%tm_min(x)@int@the minute
 The `tm_min` function interprets its argument as a time, in seconds from
 1 Jan 2000.  It returns the minute (an integer in the range 0--59) as a real.
4 tm_mon
?expressions tm_mon
?functions tm_mon
#tm\_mon(x) & int & the month \\
%tm_mon(x)@int@the month
 The `tm_mon` function interprets its argument as a time, in seconds from
 1 Jan 2000.  It returns the month (an integer in the range 1--12) as a real.
4 tm_sec
?expressions tm_sec
?functions tm_sec
#tm\_sec(x) & int & the second \\
%tm_sec(x)@int@the second
 The `tm_sec` function interprets its argument as a time, in seconds from
 1 Jan 2000.  It returns the second (an integer in the range 0--59) as a real.
4 tm_wday
?expressions tm_wday
?functions tm_wday
#tm\_wday(x) & int & the day of the week \\
%tm_wday(x)@int@the day of the week
 The `tm_wday` function interprets its argument as a time, in seconds from
 1 Jan 2000.  It returns the day of the week (an integer in the range 1--7) as
 a real.
4 tm_yday
?expressions tm_yday
?functions tm_yday
#tm\_yday(x) & int & the day of the year \\
%tm_yday(x)@int@the day of the year
 The `tm_yday` function interprets its argument as a time, in seconds from
 1 Jan 2000.  It returns the day of the year (an integer in the range 1--366)
 as a real.
4 tm_year
?expressions tm_year
?functions tm_year
#tm\_year(x) & int & the year \\
%tm_year(x)@int@the year
 The `tm_year` function interprets its argument as a time, in seconds from
 1 Jan 2000.  It returns the year (an integer) as a real.
4 valid
?expressions functions valid
?functions valid
?valid
#valid(x) & int & test validity of $\mbox{column}(x)$ during datafile manip.\\
%valid(x)@int@ test validity of column($x$) during datafile manip.
 `valid(x)` may be used only in expressions as part of `using` manipulations
 to fits or datafile plots.  See `plot datafile using`.
@end table
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/airfoil.html">Use of functions and complex variables for airfoils </a>
3 Operators
?expressions operators
?operators
 The operators in `gnuplot` are the same as the corresponding operators in the
 C programming language, except that all operators accept integer, real, and
 complex arguments, unless otherwise noted.  The ** operator (exponentiation)
 is supported, as in FORTRAN.

 Parentheses may be used to change order of evaluation.
4 Unary
?expressions operators unary
?operators unary
?unary
 The following is a list of all the unary operators and their usages:

@start table - first is interactive cleartext form
     Symbol      Example    Explanation
       -           -a          unary minus
       +           +a          unary plus (no-operation)
       ~           ~a        * one's complement
       !           !a        * logical negation
       !           a!        * factorial
       $           $3        * call arg/column during `using` manipulation
#\begin{tabular}{|ccl|} \hline
#\multicolumn{3}{|c|}{Unary Operators}\\ \hline \hline
#Symbol & Example & Explanation \\ \hline
#\verb@-@ & \verb@-a@ & unary minus \\
#\verb@+@ & \verb@+a@ & unary plus (no-operation) \\
#\verb@~@ & \verb@~a@ & * one's complement \\
#\verb@!@ & \verb@!a@ & * logical negation \\
#\verb@!@ & \verb@a!@ & * factorial \\
#\verb@$@ & \verb@$3@ & * call arg/column during `using` manipulation \\
C ugly hack: doc2ms uses $ as delimiter for eqn's so it doesn't seem to
C be able to print them. So we have to typeset this table without using
C eqn (at least that's the only solution I found, without any real docs
C on *roff and eqn
C First, terminate the table doc2ms.c already started:
%.TE
C ... then turn off eqn delimiters:
%.EQ
%delim off
%.EN
C ... and restart the table:
%.TS
%center box tab (@) ;
%c c l .
%Symbol@Example@Explanation
%_
%-@-a@unary minus
%+@+a@unary plus (no-operation)
%~@~a@* one's complement
%!@!a@* logical negation
%!@a!@* factorial
%$@$3@* call arg/column during `using` manipulation
%_
@end table
 (*) Starred explanations indicate that the operator requires an integer
 argument.

 Operator precedence is the same as in Fortran and C.  As in those languages,
 parentheses may be used to change the order of operation.  Thus -2**2 = -4,
 but (-2)**2 = 4.

 The factorial operator returns a real number to allow a greater range.
4 Binary
?expressions operators binary
?operators binary
?binary
 The following is a list of all the binary operators and their usages:

@start table - first is interactive cleartext form
     Symbol       Example      Explanation
       **          a**b          exponentiation
       *           a*b           multiplication
       /           a/b           division
       %           a%b         * modulo
       +           a+b           addition
       -           a-b           subtraction
       ==          a==b          equality
       !=          a!=b          inequality
       <           a<b           less than
       <=          a<=b          less than or equal to
       >           a>b           greater than
       >=          a>=b          greater than or equal to
       &           a&b         * bitwise AND
       ^           a^b         * bitwise exclusive OR
       |           a|b         * bitwise inclusive OR
       &&          a&&b        * logical AND
       ||          a||b        * logical OR
#\begin{tabular}{|ccl|} \hline
#\multicolumn{3}{|c|}{Binary Operators} \\ \hline \hline
#Symbol & Example & Explanation \\ \hline
#\verb~**~ & \verb~a**b~ & exponentiation\\
#\verb~*~ & \verb~a*b~ & multiplication\\
#\verb~/~ & \verb~a/b~ & division\\
#\verb~%~ & \verb~a%b~ & * modulo\\
#\verb~+~ & \verb~a+b~ & addition\\
#\verb~-~ & \verb~a-b~ & subtraction\\
#\verb~==~ & \verb~a==b~ & equality\\
#\verb~!=~ & \verb~a!=b~ & inequality\\
#\verb~<~ & \verb~a<b~ & less than\\
#\verb~<=~ & \verb~a<=b~ & less than or equal to\\
#\verb~>~ & \verb~a>b~ & greater than\\
#\verb~>=~ & \verb~a>=b~ & greater than or equal to\\
#\verb~&~ & \verb~a&b~ & * bitwise AND\\
#\verb~^~ & \verb~a^b~ & * bitwise exclusive OR\\
#\verb~|~ & \verb~a|b~ & * bitwise inclusive OR\\
#\verb~&&~ & \verb~a&&b~ & * logical AND\\
#\verb~||~ & \verb~a||b~ & * logical OR\\
%c c l .
%Symbol@Example@Explanation
%_
%**@a**b@exponentiation
%*@a*b@multiplication
%/@a/b@division
%%@a%b@* modulo
%+@a+b@addition
%-@a-b@subtraction
%==@a==b@equality
%!=@a!=b@inequality
%<@a<b@less than
%<=@a<=b@less than or equal to
%>@a>b@greater than
%>=@a>=b@greater than or equal to
%&@a&b@* bitwise AND
%^@a^b@* bitwise exclusive OR
%|@a|b@* bitwise inclusive OR
%&&@a&&b@* logical AND
%||@a||b@* logical OR

@end table
 (*) Starred explanations indicate that the operator requires integer
 arguments.

 Logical AND (&&) and OR (||) short-circuit the way they do in C.  That is,
 the second `&&` operand is not evaluated if the first is false; the second
 `||` operand is not evaluated if the first is true.
4 Ternary
?expressions operators ternary
?operators ternary
?ternary
 There is a single ternary operator:

@start table - first is interactive cleartext form
     Symbol       Example      Explanation
       ?:          a?b:c     ternary operation
#\begin{tabular}{|ccl|} \hline
#\multicolumn{3}{|c|}{Ternary Operator} \\ \hline \hline
#Symbol & Example & Explanation \\ \hline
#\verb~?:~ & \verb~a?b:c~ & ternary operation\\
%c c l .
%Symbol@Example@Explanation
%_
%?:@a?b:c@* ternary operation

@end table
 The ternary operator behaves as it does in C.  The first argument (a), which
 must be an integer, is evaluated.  If it is true (non-zero), the second
 argument (b) is evaluated and returned; otherwise the third argument (c) is
 evaluated and returned.

 The ternary operator is very useful both in constructing piecewise functions
 and in plotting points only when certain conditions are met.

 Examples:

 Plot a function that is to equal sin(x) for 0 <= x < 1, 1/x for 1 <= x < 2,
 and undefined elsewhere:
       f(x) = 0<=x && x<1 ? sin(x) : 1<=x && x<2 ? 1/x : 1/0
       plot f(x)
^ <img align=bottom src="http://www.nas.nasa.gov/~woo/gnuplot/doc/ternary.gif" alt="[ternary.gif]" width=640 height=480>
 Note that `gnuplot` quietly ignores undefined values, so the final branch of
 the function (1/0) will produce no plottable points.  Note also that f(x)
 will be plotted as a continuous function across the discontinuity if a line
 style is used.  To plot it discontinuously, create separate functions for the
 two pieces.  (Parametric functions are also useful for this purpose.)

 For data in a file, plot the average of the data in columns 2 and 3 against
 the datum in column 1, but only if the datum in column 4 is non-negative:

       plot 'file' using 1:( $4<0 ? 1/0 : ($2+$3)/2 )

 Please see `plot data-file using` for an explanation of the `using` syntax.
3 User-defined
?expressions user-defined
?user-defined
?variables
 New user-defined variables and functions of one through five variables may
 be declared and used anywhere, including on the `plot` command itself.

 User-defined function syntax:
       <func-name>( <dummy1> {,<dummy2>} ... {,<dummy5>} ) = <expression>

 where <expression> is defined in terms of <dummy1> through <dummy5>.

 User-defined variable syntax:
       <variable-name> = <constant-expression>

 Examples:
       w = 2
       q = floor(tan(pi/2 - 0.1))
       f(x) = sin(w*x)
       sinc(x) = sin(pi*x)/(pi*x)
       delta(t) = (t == 0)
       ramp(t) = (t > 0) ? t : 0
       min(a,b) = (a < b) ? a : b
       comb(n,k) = n!/(k!*(n-k)!)
       len3d(x,y,z) = sqrt(x*x+y*y+z*z)
       plot f(x) = sin(x*a), a = 0.2, f(x), a = 0.4, f(x)

^ <img align=bottom src="http://www.nas.nasa.gov/~woo/gnuplot/doc/userdefined.gif" alt="[userdefined.gif]" width=640 height=480>
 Note that the variable `pi` is already defined.  But it is in no way magic;
 you may redefine it to be whatever you like.

 Valid names are the same as in most programming languages: they must begin
 with a letter, but subsequent characters may be letters, digits, "$", or "_".
 Note, however, that the `fit` mechanism uses several variables with names
 that begin "FIT_".  It is safest to avoid using such names.  "FIT_LIMIT",
 however, is one that you may wish to redefine. See the documentation
 on `fit` for details.


 See `show functions`, `show variables`, and `fit`.
2 Glossary
?glossary
 Throughout this document an attempt has been made to maintain consistency of
 nomenclature.  This cannot be wholly successful because as `gnuplot` has
 evolved over time, certain command and keyword names have been adopted that
 preclude such perfection.  This section contains explanations of the way
 some of these terms are used.

 A "page" or "screen" is the entire area addressable by `gnuplot`.  On a
 monitor, it is the full screen; on a plotter, it is a single sheet of paper.

 A screen may contain one or more "plots".  A plot is defined by an abscissa
 and an ordinate, although these need not actually appear on it, as well as
 the margins and any text written therein.

 A plot contains one "graph".  A graph is defined by an abscissa and an
 ordinate, although these need not actually appear on it.

 A graph may contain one or more "lines".  A line is a single function or
 data set.  "Line" is also a plotting style.  The word will also be used in
 sense "a line of text".  Presumably the context will remove any ambiguity.

 The lines on a graph may have individual names.  These may be listed
 together with a sample of the plotting style used to represent them in
 the "key", sometimes also called the "legend".

 The word "title" occurs with multiple meanings in `gnuplot`.  In this
 document, it will always be preceded by the adjective "plot", "line", or
 "key" to differentiate among them.

 A graph may have up to four labelled axes.  Various commands have the name of
 an axis built into their names, such as `set xlabel`.  Other commands have
 one or more axis names as options, such as `set logscale xy`.  The names of
 the four axes for these usages are "x" for the axis along the bottom border
 of the plot, "y" for the left border, "x2" for the top border, and "y2" for
 the right border.  "z" also occurs in commands used with 3-d plotting.

 When discussing data files, the term "record" will be resurrected and used
 to denote a single line of text in the file, that is, the characters between
 newline or end-of-record characters.  A "point" is the datum extracted from
 a single record.  A "datablock" is a set of points from consecutive records,
 delimited by blank records.  A line, when referred to in the context of a
 data file, is a subset of a datablock.
2 Plotting
?plotting
 There are three `gnuplot` commands which actually create a plot: `plot`,
 `splot` and `replot`.  `plot` generates 2-d plots, `splot` generates 3-d
 plots (actually 2-d projections, of course), and `replot` appends its
 arguments to the previous `plot` or `splot` and executes the modified
 command.

 Much of the general information about plotting can be found in the discussion
 of `plot`; information specific to 3-d can be found in the `splot` section.

 `plot` operates in either rectangular or polar coordinates -- see `set polar`
 for details of the latter.  `splot` operates only in rectangular coordinates,
 but the `set mapping` command allows for a few other coordinate systems to be
 treated.  In addition, the `using` option allows both `plot` and `splot` to
 treat almost any coordinate system you'd care to define.

 `splot` can plot surfaces and contours in addition to points and/or lines.
 In addition to `splot`, see `set isosamples` for information about defining
 the grid for a 3-d function;  `splot datafile` for information about the
 requisite file structure for 3-d data values; and `set contour` and `set
 cntrparam` for information about contours.
2 Start-up
?startup
?start
?.gnuplot
 When `gnuplot` is run, it looks for an initialization file to load.  This
 file is called `.gnuplot` on Unix and AmigaOS systems, and `GNUPLOT.INI` on
 other systems.  If this file is not found in the current directory, the
 program will look for it in the home directory (under AmigaOS,
 Atari(single)TOS, MS-DOS and OS/2, the environment variable `gnuplot` should
 contain the name of this directory).  Note: if NOCWDRC is defined during the
 installation, `gnuplot` will not read from the current directory.

 If the initialization file is found, `gnuplot` executes the commands in it.
 These may be any legal `gnuplot` commands, but typically they are limited to
 setting the terminal and defining frequently-used functions or variables.
2 Substitution
?substitution
 Command-line substitution is specified by a system command enclosed in
 backquotes.  This command is spawned and the output it produces replaces
 the name of the command (and backquotes) on the command line.  Some
 implementations also support pipes;  see `plot data-file special-filenames`.

 Newlines in the output produced by the spawned command are replaced with
 blanks.

 Command-line substitution can be used anywhere on the `gnuplot` command
 line.

 Example:

 This will run the program `leastsq` and replace `leastsq` (including
 backquotes) on the command line with its output:
       f(x) = `leastsq`

 or, in VMS
       f(x) = `run leastsq`
2 Syntax
?syntax
?specify
?punctuation
 The general rules of syntax and punctuation in `gnuplot` are that keywords
 and options are order-dependent.  Options and any accompanying parameters are
 separated by spaces whereas lists and coordinates are separated by commas.
 Ranges are separated by colons and enclosed in brackets [], text and file
 names are enclosed in quotes, and a few miscellaneous things are enclosed
 in parentheses.  Braces {} are used for a few special purposes.

 Commas are used to separate coordinates on the `set` commands `arrow`,
 `key`, and `label`; the list of variables being fitted (the list after the
 `via` keyword on the `fit` command); lists of discrete contours or the loop
 parameters which specify them on the `set cntrparam` command; the arguments
 of the `set` commands `dgrid3d`, `dummy`, `isosamples`, `offsets`, `origin`,
 `samples`, `size`, `time`, and `view`; lists of tics or the loop parameters
 which specify them; the offsets for titles and axis labels; parametric
 functions to be used to calculate the x, y, and z coordinates on the `plot`,
 `replot` and `splot` commands; and the complete sets of keywords specifying
 individual plots (data sets or functions) on the `plot`, `replot` and `splot`
 commands.

 Parentheses are used to delimit sets of explicit tics (as opposed to loop
 parameters) and to indicate computations in the `using` filter of the `fit`,
 `plot`, `replot` and `splot` commands.

 (Parentheses and commas are also used as usual in function notation.)

 Brackets are used to delimit ranges, whether they are given on `set`, `plot`
 or `splot` commands.

 Colons are used to separate extrema in `range` specifications (whether they
 are given on `set`, `plot` or `splot` commands) and to separate entries in
 the `using` filter of the `plot`, `replot`, `splot` and `fit` commands.

 Semicolons are used to separate commands given on a single command line.

 Braces are used in text to be specially processed by some terminals, like
 `postscript`.  They are also used to denote complex numbers: {3,2} = 3 + 2i.

 Text may be enclosed in single- or double-quotes.  Backslash processing of
 sequences like \n (newline) and \345 (octal character code) is performed for
 double-quoted strings, but not for single-quoted strings.

 The justification is the same for each line of a multi-line string.  Thus the
 center-justified string
       "This is the first line of text.\nThis is the second line."
 will produce
                        This is the first line of text.
                           This is the second line.
 but
       'This is the first line of text.\nThis is the second line.'
 will produce
           This is the first line of text.\nThis is the second line.

 Filenames may be entered with either single- or double-quotes.  In this
 manual the command examples generally single-quote filenames and double-quote
 other string tokens for clarity.

 At present you should not embed \n inside {} when using the enhanced option
 of the postscript terminal.

 The EEPIC, Imagen, Uniplex, LaTeX, and TPIC drivers allow a newline to be
 specified by \\ in a single-quoted string or \\\\ in a double-quoted string.

 Back-quotes are used to enclose system commands for substitution.
2 Time/Date data
?time/date
 `gnuplot` supports the use of time and/or date information as input data.
 This feature is activated by the commands `set xdata time`, `set ydata time`,
 etc.

 Internally all times and dates are converted to the number of seconds from
 the year 2000.  The command `set timefmt` defines the format for all inputs:
 data files, ranges, tics, label positions---in short, anything that accepts a
 data value must receive it in this format.  Since only one input format can
 be in force at a given time, all time/date quantities being input at the same
 time must be presented in the same format.  Thus if both x and y data in a
 file are time/date, they must be in the same format.

 The conversion to and from seconds assumes Universal Time (which is the same
 as Greenwich Standard Time).  There is no provision for changing the time
 zone or for daylight savings.  If all your data refer to the same time zone
 (and are all either daylight or standard) you don't need to worry about these
 things.  But if the absolute time is crucial for your application, you'll
 need to convert to UT yourself.

 Commands like `show xrange` will re-interpret the integer according to
 `timefmt`.  If you change `timefmt`, and then `show` the quantity again, it
 will be displayed in the new `timefmt`.  For that matter, if you give the
 deactivation command (like `set xdata`), the quantity will be shown in its
 numerical form.

 The command `set format` defines the format that will be used for tic labels,
 whether or not the specified axis is time/date.

 If time/date information is to be plotted from a file, the `using` option
 _must_ be used on the `plot` or `splot` command.  These commands simply use
 white space to separate columns, but white space may be embedded within the
 time/date string.  If you use tabs as a separator, some trial-and-error may
 be necessary to discover how your system treats them.

 The following example demonstrates time/date plotting.

 Suppose the file "data" contains records like

       03/21/95 10:00  6.02e23

 This file can be plotted by

       set xdata time
       set timefmt "%m/%d/%y"
       set xrange ["03/21/95":"03/22/95"]
       set format x "%m/%d"
       set timefmt "%m/%d/%y %H:%M"
       plot "data" using 1:3

 which will produce xtic labels that look like "03/21".

 See the descriptions of each command for more details.
1 Commands
?commands
 This section lists the commands acceptable to `gnuplot` in alphabetical
 order.  Printed versions of this document contain all commands; on-line
 versions may not be complete.  Indeed, on some systems there may be no
 commands at all listed under this heading.

 Note that in most cases unambiguous abbreviations for command names and their
 options are permissible, i.e., "`p f(x) w l`" instead of "`plot f(x) with
 lines`".

 In the syntax descriptions, braces ({}) denote optional arguments and a
 vertical bar (|) separates mutually exclusive choices.
2 cd
?commands cd
?cd
 The `cd` command changes the working directory.

 Syntax:
       cd '<directory-name>'

 The directory name must be enclosed in quotes.

 Examples:
       cd 'subdir'
       cd ".."

 DOS users _must_ use single-quotes---backslash [\] has special significance
 inside double-quotes.  For example,
       cd "c:\newdata"
 fails, but
       cd 'c:\newdata'
 works as expected.
2 call
?commands call
?call
 The `call` command is identical to the load command with one exception: you
 can have up to ten additional parameters to the command (delimited according
 to the standard parser rules) which can be substituted into the lines read
 from the file.  As each line is read from the `call`ed input file, it is
 scanned for the sequence `$` (dollar-sign) followed by a digit (0--9).  If
 found, the sequence is replaced by the corresponding parameter from the
 `call` command line.  If the parameter was specified as a string in the
 `call` line, it is substituted without its enclosing quotes.  `$` followed by
 any character other than a digit will be that character.  E.g. use `$$` to
 get a single `$`.  Providing more than ten parameters on the `call` command
 line will cause an error.  A parameter that was not provided substitutes as
 nothing.  Files being `call`ed may themselves contain `call` or `load`
 commands.

 The `call` command _must_ be the last command on a multi-command line.

 Syntax:
       call "<input-file>" <parameter-0> <parm-1> ... <parm-9>

 The name of the input file must be enclosed in quotes, and it is recommended
 that parameters are similarly enclosed in quotes (future versions of gnuplot
 may treat quoted and unquoted arguments differently).

 Example:

 If the file 'calltest.gp' contains the line:
       print "p0=$0 p1=$1 p2=$2 p3=$3 p4=$4 p5=$5 p6=$6 p7=x$7x"

 entering the command:
       call 'calltest.gp' "abcd" 1.2 + "'quoted'" -- "$2"

 will display:
       p0=abcd p1=1.2 p2=+ p3='quoted' p4=- p5=- p6=$2 p7=xx

 NOTE: there is a clash in syntax with the datafile `using` callback
 operator.  Use `$$n` or `column(n)` to access column n from a datafile inside
 a `call`ed datafile plot.
2 clear
?commands clear
?clear
 The `clear` command erases the current screen or output device as specified
 by `set output`.  This usually generates a formfeed on hardcopy devices.  Use
 `set terminal` to set the device type.

 For some terminals `clear` erases only the portion of the plotting surface
 defined by `set size`, so for these it can be used in conjunction with `set
 multiplot` to create an inset.

 Example:
       set multiplot
       plot sin(x)
       set origin 0.5,0.5
       set size 0.4,0.4
       clear
       plot cos(x)
       set nomultiplot

 Please see `set multiplot`, `set size`, and `set origin` for details of these
 commands.
2 exit
?commands exit
?exit
 The commands `exit` and `quit` and the END-OF-FILE character will exit the
 current `gnuplot` command file and `load` the next one.  See "help
 batch/interactive" for more details.

 Each of these commands will clear the output device (as does the `clear`
 command) before exiting.
2 fit
?commands fit
?fit
?least-squares
?Marquardt
 The `fit` command can fit a user-defined function to a set of data points
 (x,y) or (x,y,z), using an implementation of the nonlinear least-squares
 (NLLS) Marquardt-Levenberg algorithm.  Any user-defined variable occurring in
 the function body may serve as a fit parameter, but the return type of the
 function must be real.

 Syntax:
       fit {[xrange] {[yrange]}} <function> '<datafile>'
           {datafile-modifiers}
           via '<parameter file>' | <var1>{,<var2>,...}

 Ranges may be specified to temporarily limit the data which is to be fitted;
 any out-of-range data points are ignored. The syntax is
       [{dummy_variable=}{<min>}{:<max>}],
 analogous to `plot`; see `plot ranges`.

 <function> is any valid `gnuplot` expression, although it is usual to use a
 previously user-defined function of the form f(x) or f(x,y).

 <datafile> is treated as in the `plot` command.  All the `plot datafile`
 modifiers (`using`, `every`,...) except `smooth` are applicable to `fit`.
 See `plot datafile`.

 The default data formats for fitting functions with a single independent
 variable, y=f(x), are {x:}y or x:y:s; those formats can be changed with
 the datafile `using` qualifier.  The third item, (a column number or an
 expression), if present, is interpreted as the standard deviation of the
 corresponding y value and is used to compute a weight for the datum, 1/s**2.
 Otherwise, all data points are weighted equally, with a weight of one.

 To fit a function with two independent variables, z=f(x,y), the required
 format is `using` with four items, x:y:z:s.  The complete format must be
 given---no default columns are assumed for a missing token.  Weights for
 each data point are evaluated from 's' as above.  If error estimates are
 not available, a constant value can be specified as a constant expression
 (see `plot datafile using`), e.g., `using 1:2:3:(1)`.

 Multiple datasets may be simultaneously fit with functions of one
 independent variable by making y a 'pseudo-variable', e.g., the dataline
 number, and fitting as two independent variables.  See `fit multibranch`.

 The `via` qualifier specifies which parameters are to be adjusted, either
 directly, or by referencing a parameter file.

 Examples:
       f(x) = a*x**2 + b*x + c
       g(x,y) = a*x**2 + b*y**2 + c*x*y
       FIT_LIMIT = 1e-6
       fit f(x) 'measured.dat' via 'start.par'
       fit f(x) 'measured.dat' using 3:($7-5) via 'start.par'
       fit f(x) './data/trash.dat' using 1:2:3 via a, b, c
       fit g(x,y) 'surface.dat' using 1:2:3:(1) via a, b, c

 After each iteration step, detailed information about the current state
 of the fit is written to the display.  The same information about the
 initial and final states is written to a log file, "fit.log".  This file
 is always appended to, so as to not lose any previous fit history;  it
 should be deleted or renamed as desired.

 The fit may be interrupted by pressing Ctrl-C (any key but Ctrl-C under
 MSDOS and Atari Multitasking Systems).  After the current iteration
 completes, you have the option to (1) stop the fit and accept the current
 parameter values, (2) continue the fit, (3) execute a `gnuplot` command
 as specified by the environment variable FIT_SCRIPT.  The default for
 FIT_SCRIPT is `replot`, so if you had previously plotted both the data
 and the fitting function in one graph, you can display the current state
 of the fit.

 Once `fit` has finished, the `update` command may be used to store final
 values in a file for subsequent use as a parameter file.   See `update`
 for details.
3 adjustable parameters
?commands fit parameters
?fit parameters
?commands fit adjustable_parameters
?fit adjustable_parameters
?fit_parameters
 There are two ways that `via` can specify the parameters to be adjusted,
 either directly on the command line or indirectly, by referencing a
 parameter file.  The two use different means to set initial values.

 Adjustable parameters can be specified by a comma-separated list of variable
 names after the `via` keyword.  Any variable that is not already defined is
 is created with an initial value of 1.0.  However, the fit is more likely
 to converge rapidly if the variables have been previously declared with more
 appropriate starting values.

 In a parameter file, each parameter to be varied and a corresponding initial
 value are specified, one per line, in the form
       varname = value

 Comments, marked by '#', and blank lines are permissible.  The
 special form
       varname = value       # FIXED

 means that the variable is treated as a 'fixed parameter', initialized by the
 parameter file, but not adjusted by `fit`.  For clarity, it may be useful to
 designate variables as fixed parameters so that their values are reported by
 `fit`.  The keyword `# FIXED` has to appear in exactly this form.

3 beginner's guide
?commands fit beginners_guide
?fit beginners_guide
?fit guide
?fitting
 `fit` is used to find a set of parameters that 'best' fits your data to your
 user-defined function.  The fit is judged on the basis of the the sum of the
 squared differences or 'residuals' (SSR) between the input data points and
 the function values, evaluated at the same places.  This quantity is often
 called 'chisquare' (i.e., the Greek letter chi, to the power of 2).  The
 algorithm attempts to minimize SSR, or more precisely, WSSR, as the residuals
 are 'weighted' by the input data errors (or 1.0) before being squared; see
 `fit error_estimates` for details.

 That's why it is called 'least-squares fitting'.  Let's look at an example
 to see what is meant by 'non-linear', but first we had better go over some
 terms.  Here it is convenient to use z as the dependent variable for
 user-defined functions of either one independent variable, z=f(x), or two
 independent variables, z=f(x,y).  A parameter is a user-defined variable
 that `fit` will adjust, i.e., an unknown quantity in the function
 declaration.  Linearity/non-linearity refers to the relationship of the
 dependent variable, z, to the parameters which `fit` is adjusting, not of
 z to the independent variables, x and/or y.  (To be technical, the
 second {and higher} derivatives of the fitting function with respect to
 the parameters are zero for a linear least-squares problem).

 For linear least-squares (LLS), the user-defined function will be a sum of
 simple functions, not involving any parameters, each multiplied by one
 parameter.  NLLS handles more complicated functions in which parameters can
 be used in a large number of ways.  An example that illustrates the
 difference between linear and nonlinear least-squares is the Fourier series.
 One member may be written as
      z=a*sin(c*x) + b*cos(c*x).
 If a and b are the unknown parameters and c is constant, then estimating
 values of the parameters is a linear least-squares problem.  However, if
 c is an unknown parameter, the problem is nonlinear.

 In the linear case, parameter values can be determined by comparatively
 simple linear algebra, in one direct step.  However LLS is a special case
 which is also solved along with more general NLLS problems by the iterative
 procedure that `gnuplot` uses.  `fit` attempts to find the minimum by doing
 a search.  Each step (iteration) calculates WSSR with a new set of parameter
 values.  The Marquardt-Levenberg algorithm selects the parameter values for
 the next iteration.  The process continues until a preset criterium is met,
 either (1) the fit has "converged" (the relative change in WSSR is less than
 FIT_LIMIT), or (2) it reaches a preset iteration count limit, FIT_MAXITER
 (see `fit control variables`).  The fit may also be interrupted
 and subsequently halted from the keyboard (see `fit`).

 Often the function to be fitted will be based on a model (or theory) that
 attempts to describe or predict the behaviour of the data.  Then `fit` can
 be used to find values for the free parameters of the model, to determine
 how well the data fits the model, and to estimate an error range for each
 parameter.  See `fit error_estimates`.

 Alternatively, in curve-fitting, functions are selected independent of
 a model (on the basis of experience as to which are likely to describe
 the trend of the data with the desired resolution and a minimum number
 of parameters*functions.)  The `fit` solution then provides an analytic
 representation of the curve.

 However, if all you really want is a smooth curve through your data points,
 the `smooth` option to `plot` may be what you've been looking for rather
 than `fit`.
3 error estimates
?commands fit error_estimate
?fit error_estimate
?fit errors
 In `fit`, the term "error" is used in two different contexts, data error
 estimates and parameter error estimates.

 Data error estimates are used to calculate the relative weight of each data
 point when determining the weighted sum of squared residuals, WSSR or
 chisquare.  They can affect the parameter estimates, since they determine
 how much influence the deviation of each data point from the fitted function
 has on the final values.  Some of the `fit` output information, including
 the parameter error estimates, is more meaningful if accurate data error
 estimates have been provided.

 The 'statistical overview' describes some of the `fit` output and gives some
 background for the 'practical guidelines'.
4 statistical overview
?commands fit error statistical_overview
?fit error statistical_overview
?statistical_overview
 The theory of non-linear least-squares (NLLS) is generally described in terms
 of a normal distribution of errors, that is, the input data is assumed to be
 a sample from a population having a given mean and a Gaussian (normal)
 distribution about the mean with a given standard deviation.  For a sample of
 sufficiently large size, and knowing the population standard deviation, one
 can use the statistics of the chisquare distribution to describe a "goodness
 of fit" by looking at the variable often called "chisquare".  Here, it is
 sufficient to say that a reduced chisquare (chisquare/degrees of freedom,
 where degrees of freedom is the number of datapoints less the number of
 parameters being fitted) of 1.0 is an indication that the weighted sum of
 squared deviations between the fitted function and the data points is the
 same as that expected for a random sample from a population characterized by
 the function with the current value of the parameters and the given standard
 deviations.

 If the standard deviation for the population is not constant, as in counting
 statistics where variance = counts, then each point should be individually
 weighted when comparing the observed sum of deviations and the expected sum
 of deviations.

 At the conclusion `fit` reports 'stdfit', the standard deviation of the fit,
 which is the rms of the residuals, and the variance of the residuals, also
 called 'reduced chisquare' when the data points are weighted.  The number of
 degrees of freedom (the number of data points minus the number of fitted
 parameters) is used in these estimates because the parameters used in
 calculating the residuals of the datapoints were obtained from the same data.

 To estimate confidence levels for the parameters, one can use the minimum
 chisquare obtained from the fit and chisquare statistics to determine the
 value of chisquare corresponding to the desired confidence level, but
 considerably more calculation is required to determine the combinations of
 parameters which produce such values.

 Rather than determine confidence intervals, `fit` reports parameter error
 estimates which are readily obtained from the variance-covariance matrix
 after the final iteration.  By convention, these estimates are called
 "standard errors" or "asymptotic standard errors", since they are calculated
 in the same way as the standard errors (standard deviation of each parameter)
 of a linear least-squares problem, even though the statistical conditions for
 designating the quantity calculated to be a standard deviation are not
 generally valid for the NLLS problem.  The asymptotic standard errors are
 generally over-optimistic and should not be used for determining confidence
 levels, but are useful for qualitative purposes.

 The final solution also produces a correlation matrix, which gives an
 indication of the correlation of parameters in the region of the solution;
 if one parameter is changed, increasing chisquare, does changing another
 compensate?  The main diagonal elements, autocorrelation, are all 1; if
 all parameters were independent, all other elements would be nearly 0.  Two
 variables which completely compensate each other would have an off-diagonal
 element of unit magnitude, with a sign depending on whether the relation is
 proportional or inversely proportional.  The smaller the magnitudes of the
 off-diagonal elements, the closer the estimates of the standard deviation
 of each parameter would be to the asymptotic standard error.
4 practical guidelines
?commands fit error practical_guidelines
?fit error practical_guidelines
?practical_guidelines
?guidelines
 If you have a basis for assigning weights to each data point, doing so lets
 you make use of additional knowledge about your measurements, e.g., take into
 account that some points may be more reliable than others.  That may affect
 the final values of the parameters.

 Weighting the data provides a basis for interpreting the additional `fit`
 output after the last iteration.  Even if you weight each point equally,
 estimating an average standard deviation rather than using a weight of 1
 makes WSSR a dimensionless variable, as chisquare is by definition.

 Each fit iteration will display information which can be used to evaluate
 the progress of the fit.  (An '*' indicates that it did not find a smaller
 WSSR and is trying again.)  The 'sum of squares of residuals', also called
 'chisquare', is the WSSR between the data and your fitted function; `fit`
 has minimized that.  At this stage, with weighted data, chisquare is expected
 to approach the number of degrees of freedom (data points minus parameters).
 The WSSR can be used to calculate the reduced chisquare (WSSR/ndf) or stdfit,
 the standard deviation of the fit, sqrt(WSSR/ndf).  Both of these are
 reported for the final WSSR.

 If the data are unweighted, stdfit is the rms value of the deviation of the
 data from the fitted function, in user units.

 If you supplied valid data errors, the number of data points is large enough,
 and the model is correct, the reduced chisquare should be about unity.  (For
 details, look up the 'chi-squared distribution' in your favourite statistics
 reference.)  If so, there are additional tests, beyond the scope of this
 overview, for determining how well the model fits the data.

 A reduced chisquare much larger than 1.0 may be due to incorrect data error
 estimates, data errors not normally distributed, systematic measurement
 errors, 'outliers', or an incorrect model function.  A plot of the residuals,
 e.g., `plot 'datafile' using 1:($2-f($1))`, may help to show any systematic
 trends.  Plotting both the data points and the function may help to suggest
 another model.

 Similarly, a reduced chisquare less than 1.0 indicates WSSR is less than that
 expected for a random sample from the function with normally distributed
 errors.  The data error estimates may be too large, the statistical
 assumptions may not be justified, or the model function may be too general,
 fitting fluctuations in a particular sample in addition to the underlying
 trends.  In the latter case, a simpler function may be more appropriate.

 You'll have to get used to both `fit` and the kind of problems you apply it
 to before you can relate the standard errors to some more practical estimates
 of parameter uncertainties or evaluate the significance of the correlation
 matrix.

 Note that `fit`, in common with most NLLS implementations, minimizes the
 weighted sum of squared distances (y-f(x))**2.  It does not provide any means
 to account for "errors" in the values of x, only in y.  Also, any "outliers"
 (data points outside the normal distribution of the model) will have an
 exaggerated effect on the solution.
3 fit controlling
?commands fit_control
?fit_control
?fit control
 There are a number of `gnuplot` variables that can be defined to affect
 `fit`.  Those which can be defined once `gnuplot` is running are listed
 under 'control_variables' while those defined before starting `gnuplot`
 are listed under 'environment_variables'.
4 control variables
?commands fit_control variables
?fit_control variables
?fit control variables
 The default epsilon limit (1e-5) may be changed by declaring a value for
       FIT_LIMIT
 When the sum of squared residuals changes between two iteration steps by
 a factor less than this number (epsilon), the fit is considered to have
 'converged'.

 The maximum number of iterations may be limited by declaring a value for
       FIT_MAXITER
 A value of 0 (or not defining it at all)  means that there is no limit.

 If you need even more control about the algorithm, and know the
 Marquardt-Levenberg algorithm well, there are some more variables to
 influence it. The startup value of `lambda` is normally calculated
 automatically from the ML-matrix, but if you want to, you may provide
 your own one with
       FIT_START_LAMBDA
 Specifying FIT_START_LAMBDA as zero or less will re-enable the automatic
 selection. The variable
       FIT_LAMBDA_FACTOR
 gives the factor by which `lambda` is increased or decreased whenever
 the chi-squared target function increased or decreased significantly.
 Setting FIT_LAMBDA_FACTOR to zero re-enables the default factor of
 10.0.

 Oher variables with the FIT_ prefix may be added to `fit`, so it is safer
 not to use that prefix for user-defined variables.

 The variables FIT_SKIP and FIT_INDEX were used by earlier releases of
 `gnuplot` with a 'fit' patch called `gnufit` and are no longer available.
 The datafile `every` modifier provides the functionality of FIT_SKIP.
 FIT_INDEX was used for multi-branch fitting, but multi-branch fitting of
 one independent variable is now done as a pseudo-3D fit in which the
 second independent variable and `using` are used to specify the branch.
 See `fit multi-branch`.
4 environment variables
?commands fit_control environment
?fit_control environment
?fit control environment
 The environment variables must be defined before `gnuplot` is executed; how
 to do so depends on your operating system.

       FIT_LOG
 changes the name (and/or path) of the file to which the fit log will be
 written from the default of "fit.log" in the working directory.

       FIT_SCRIPT
 specifies a command that may be executed after an user interrupt. The default
 is `replot`, but a `plot` or `load` command may be useful to display a plot
 customized to highlight the progress of the fit.
3 multi-branch
?commands fit multi-branch
?fit multi-branch
?multi-branch
?branch
 In multi-branch fitting, multiple data sets can be simultaneously fit with
 functions of one independent variable having common parameters by minimizing
 the total WSSR.  The function and parameters (branch) for each data set are
 selected by using a 'pseudo-variable', e.g., either the dataline number (a
 'column' index of -1) or the datafile index (-2), as the second independent
 variable.

 Example:  Given two exponential decays of the form, z=f(x), each describing
 a different data set but having a common decay time, estimate the values of
 the parameters.  If the datafile has the format x:z:s, then
      f(x,y) = (y==0) ? a*exp(-x/tau) : b*exp(-x/tau)
      fit f(x,y) 'datafile' using  1:-1:2:3  via a, b, tau

 For a more complicated example, see the file "hexa.fnc" used by the
 "fit.dem" demo.

 Appropriate weighting may be required since unit weights may cause one
 branch to predominate if there is a difference in the scale of the dependent
 variable.  Fitting each branch separately, using the multi-branch solution
 as initial values, may give an indication as to the relative effect of each
 branch on the joint solution.
3 starting values
?commands fit starting_values
?fit starting_values
?starting_values
 Nonlinear fitting is not guaranteed to converge to the global optimum (the
 solution with the smallest sum of squared residuals, SSR), and can get stuck
 at a local minimum.  The routine has no way to determine that;  it is up to
 you to judge whether this has happened.

 `fit` may, and often will get "lost" if started far from a solution, where
 SSR is large and changing slowly as the parameters are varied, or it may
 reach a numerically unstable region (e.g., too large a number causing a
 floating point overflow) which results in an "undefined value" message
 or `gnuplot` halting.

 To improve the chances of finding the global optimum, you should set the
 starting values at least roughly in the vicinity of the solution, e.g.,
 within an order of magnitude, if possible.  The closer your starting values
 are to the solution, the less chance of stopping at another minimum.  One way
 to find starting values is to plot data and the fitting function on the same
 graph and change parameter values and `replot` until reasonable similarity
 is reached.  The same plot is also useful to check whether the fit stopped at
 a minimum with a poor fit.

 Of course, a reasonably good fit is not proof there is not a "better" fit (in
 either a statistical sense, characterized by an improved goodness-of-fit
 criterion, or a physical sense, with a solution more consistent with the
 model.)  Depending on the problem, it may be desirable to `fit` with various
 sets of starting values, covering a reasonable range for each parameter.
3 tips
?commands fit tips
?fit tips
?tips
 Here are some tips to keep in mind to get the most out of `fit`.  They're not
 very organized, so you'll have to read them several times until their essence
 has sunk in.

 The two forms of the `via` argument to `fit` serve two largely distinct
 purposes.  The `via "file"` form is best used for (possibly unattended) batch
 operation, where you just supply the startup values in a file and can later
 use `update` to copy the results back into another (or the same) parameter
 file.

 The `via var1, var2, ...` form is best used interactively, where the command
 history mechanism may be used to edit the list of parameters to be fitted or
 to supply new startup values for the next try.  This is particularly useful
 for hard problems, where a direct fit to all parameters at once won't work
 without good starting values.  To find such, you can iterate several times,
 fitting only some of the parameters, until the values are close enough to the
 goal that the final fit to all parameters at once will work.

 Make sure that there is no mutual dependency among parameters of the function
 you are fitting.  For example, don't try to fit a*exp(x+b), because
 a*exp(x+b)=a*exp(b)*exp(x).  Instead, fit either a*exp(x) or exp(x+b).

 A technical issue:  the parameters must not be too different in magnitude.
 The larger the ratio of the largest and the smallest absolute parameter
 values, the slower the fit will converge.  If the ratio is close to or above
 the inverse of the machine floating point precision, it may take next to
 forever to converge, or refuse to converge at all.  You will have to adapt
 your function to avoid this, e.g., replace 'parameter' by '1e9*parameter' in
 the function definition, and divide the starting value by 1e9.

 If you can write your function as a linear combination of simple functions
 weighted by the parameters to be fitted, by all means do so.  That helps a
 lot, because the problem is no longer nonlinear and should converge with only
 a small number of iterations, perhaps just one.

 Some prescriptions for analysing data, given in practical experimentation
 courses, may have you first fit some functions to your data, perhaps in a
 multi-step process of accounting for several aspects of the underlying
 theory one by one, and then extract the information you really wanted from
 the fitting parameters of those functions.  With `fit`, this may often be
 done in one step by writing the model function directly in terms of the
 desired parameters.  Transforming data can also quite often be avoided,
 though sometimes at the cost of a more difficult fit problem.  If you think
 this contradicts the previous paragraph about simplifying the fit function,
 you are correct.

 A "singular matrix" message indicates that this implementation of the
 Marquardt-Levenberg algorithm can't calculate parameter values for the next
 iteration.  Try different starting values, writing the function in another
 form, or a simpler function.

 Finally, a nice quote from the manual of another fitting package (fudgit),
 that kind of summarizes all these issues:  "Nonlinear fitting is an art!"
2 help
?commands help
?help
 The `help` command displays on-line help. To specify information on a
 particular topic use the syntax:

       help {<topic>}

 If <topic> is not specified, a short message is printed about `gnuplot`.
 After help for the requested topic is given, a menu of subtopics is given;
 help for a subtopic may be requested by typing its name, extending the help
 request.  After that subtopic has been printed, the request may be extended
 again or you may go back one level to the previous topic.  Eventually, the
 `gnuplot` command line will return.

 If a question mark (?) is given as the topic, the list of topics currently
 available is printed on the screen.
2 if
?commands if
?if
 The `if` command allows commands to be executed conditionally.

 Syntax:
       if (<condition>) <command-line>

 <condition> will be evaluated.  If it is true (non-zero), then the command(s)
 of the <command-line> will be executed.  If <condition> is false (zero), then
 the entire <command-line> is ignored.  Note that use of `;` to allow multiple
 commands on the same line will _not_ end the conditionalized commands.

 Examples:
       pi=3
       if (pi!=acos(-1)) print "?Fixing pi!"; pi=acos(-1); print pi
 will display:
       ?Fixing pi!
       3.14159265358979
 but
       if (1==2) print "Never see this"; print "Or this either"
 will not display anything.

 See `reread` for an example of how `if` and `reread` can be used together to
 perform a loop.
2 load
?commands load
?load
 The `load` command executes each line of the specified input file as if it
 had been typed in interactively.  Files created by the `save` command can
 later be `load`ed.  Any text file containing valid commands can be created
 and then executed by the `load` command.  Files being `load`ed may themselves
 contain `load` or `call` commands.  See `comment` for information about
 comments in commands.  To `load` with arguments, see `call`.

 The `load` command _must_ be the last command on a multi-command line.

 Syntax:
       load "<input-file>"

 The name of the input file must be enclosed in quotes.

 The special filename "-" may be used to `load` commands from standard input.
 This allows a `gnuplot` command file to accept some commands from standard
 input.  Please see "help batch/interactive" for more details.

 Examples:
       load 'work.gnu'
       load "func.dat"

 The `load` command is performed implicitly on any file names given as
 arguments to `gnuplot`.  These are loaded in the order specified, and
 then `gnuplot` exits.
2 pause
?commands pause
?pause
 The `pause` command displays any text associated with the command and then
 waits a specified amount of time or until the carriage return is pressed.
 `pause` is especially useful in conjunction with `load` files.

 Syntax:
       pause <time> {"<string>"}

 <time> may be any integer constant or expression.  Choosing -1 will wait
 until a carriage return is hit, zero (0) won't pause at all, and a positive
 integer will wait the specified number of seconds.  `pause 0` is synonymous
 with `print`.

 Note: Since `pause` communicates with the operating system rather than the
 graphics, it may behave differently with different device drivers (depending
 upon how text and graphics are mixed).

 Examples:
       pause -1    # Wait until a carriage return is hit
       pause 3     # Wait three seconds
       pause -1  "Hit return to continue"
       pause 10  "Isn't this pretty?  It's a cubic spline."

2 plot
?commands plot
?plot
 `plot` is the primary command for drawing plots with `gnuplot`.  It creates
 plots of functions and data in many, many ways.  `plot` is used to draw 2-d
 functions and data; `splot` draws 2-d projections of 3-d surfaces and data.
 `plot` and `splot` contain many common features; see `splot` for differences.
 Note specifically that `splot`'s `binary` and `matrix` options do not exist
 for `plot`.

 Syntax:
       plot {<ranges>}
            {<function> | {"<datafile>" {datafile-modifiers}}}
            {axes <axes>} {<title-spec>} {with <style>}
            {, {definitions,} <function> ...}

 where either a <function> or the name of a data file enclosed in quotes is
 supplied.  A function is a mathematical expression or a pair of mathematical
 expressions in parametric mode.  The expressions may be defined completely or
 in part earlier in the stream of `gnuplot` commands (see `user-defined`).

 It is also possible to define functions and parameters on the `plot` command
 itself.  This is done merely by isolating them from other items with commas.

 There are four possible sets of axes available; the keyword <axes> is used to
 select the axes for which a particular line should be scaled.  `x1y1` refers
 to the axes on the bottom and left; `x2y2` to those on the top and right;
 `x1y2` to those on the bottom and right; and `x2y1` to those on the top and
 left.  Ranges specified on the `plot` command apply only to the first set of
 axes (bottom left).

 Examples:
       plot sin(x)
       plot f(x) = sin(x*a), a = .2, f(x), a = .4, f(x)
       plot [t=1:10] [-pi:pi*2] tan(t), \
            "data.1" using (tan($2)):($3/$4) smooth csplines \
                     axes x1y2 notitle with lines 5

3 data-file
?commands plot datafile
?plot datafile
?data-file
?datafile
?data
 Discrete data contained in a file can be displayed by specifying the name of
 the data file (enclosed in single or double quotes) on the `plot` command line.

 Syntax:
       plot '<file_name>' {index <index list>}
                             {every <every list>}
                             {thru <thru expression>}
                             {using <using list>}
                             {smooth <option>}

 The modifiers `index`, `every`, `thru`, `using`, and `smooth` are discussed
 separately.  In brief, `index` selects which data sets in a multi-data-set
 file are to be plotted, `every` specifies which points within a single data
 set are to be plotted, `using` determines how the columns within a single
 record are to be interpreted (`thru` is a special case of `using`), and
 `smooth` allows for simple interpolation and approximation.  ('splot' has a
 similar syntax, but does not support the `smooth` and `thru` options.)

 Data files should contain at least one data point per record (`using` can
 select one data point from the record).  Records beginning with `#` (and
 also with `!` on VMS) will be treated as comments and ignored.  Each data
 point represents an (x,y) pair.  For `plot`s with error bars (see `set style
 errorbars`), each data point is (x,y,ydelta), (x,y,ylow,yhigh), (x,y,xdelta),
 (x,y,xlow,xhigh), or (x,y,xlow,xhigh,ylow,yhigh).  In all cases, the numbers
 on each record of a data file must be separated by white space (one or more
 blanks or tabs), unless a format specifier is provided by the `using` option.
 This white space divides each record into columns.

 Data may be written in exponential format with the exponent preceded by the
 letter e, E, d, D, q, or Q.

 Only one column (the y value) need be provided.  If x is omitted, `gnuplot`
 provides integer values starting at 0.

 In datafiles, blank records (records with no characters other than blanks and
 a newline and/or carriage return) are significant---pairs of blank records
 separate `index`es (see `plot datafile index`).  Data separated by double
 blank records are treated as if they were in separate data files.

 Single blank records designate discontinuities in a `plot`; no line will join
 points separated by a blank records (if they are plotted with a line style).

 If autoscaling has been enabled (`set autoscale`), the axes are automatically
 extended to include all datapoints, with a whole number of tic marks if tics
 are being drawn.  This has two consequences: i) For `splot`, the corner of
 the surface may not coincide with the corner of the base.  In this case, no
 vertical line is drawn.  ii) When plotting data with the same x range on a
 dual-axis graph, the x coordinates may not coincide if the x2tics are not
 being drawn.  This is because the x axis has been autoextended to a whole
 number of tics, but the x2 axis has not.  The following example illustrates
 the problem:

       reset; plot '-', '-'
       1 1
       19 19
       e
       1 1
       19 19
       e
4 every
?commands plot datafile every
?plot datafile every
?plot every
?data-file every
?datafile every
?every
 The `every` keyword allows a periodic sampling of a data set to be plotted.

 In the discussion a "point" is a datum defined by a single record in the
 file; "block" here will mean the same thing as "datablock" (see `glossary`).

 Syntax:
       plot 'file' every {<point_incr>}
                           {:{<block_incr>}
                             {:{<start_point>}
                               {:{<start_block>}
                                 {:{<end_point>}
                                   {:<end_block>}}}}}

 The data points to be plotted are selected according to a loop from
 <`start_point`> to <`end_point`> with increment <`point_incr`> and the
 blocks according to a loop from <`start_block`> to <`end_block`> with
 increment <`block_incr`>.

 The first datum in each block is numbered '0', as is the first block in the
 file.

 Note that records containing unplottable information are counted.

 Any of the numbers can be omitted; the increments default to unity, the start
 values to the first point or block, and the end values to the last point or
 block.  If `every` is not specified, all points in all lines are plotted.

 Examples:
       every :::3::3    # selects just the fourth block ('0' is first)
       every :::::9     # selects the first 10 blocks
       every 2:2        # selects every other point in every other block
       every ::5::15    # selects points 5 through 15 in each block
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/simple.html">Simple Plot Demos </a>,
^ <a href="http://www.nas.nasa.gov/~woo/gnuplot/surfacea/surfacea.html">Non-parametric splot demos </a>, and
^ <a href="http://www.nas.nasa.gov/~woo/gnuplot/surfaceb/surfaceb.html">Parametric splot demos.</a>
4 example datafile
?commands plot datafile example
?plot datafile example
?plot example
?datafile example
?data-file example
?example
 This example plots the data in the file "population.dat" and a theoretical
 curve:

       pop(x) = 103*exp((1965-x)/10)
       plot [1960:1990] 'population.dat', pop(x)

 The file "population.dat" might contain:

       # Gnu population in Antarctica since 1965
          1965   103
          1970   55
          1975   34
          1980   24
          1985   10

^ <img align=bottom src="http://www.nas.nasa.gov/~woo/gnuplot/doc/population.gif" alt="[population.gif]" width=640 height=480>
4 index
?commands plot datafile index
?plot datafile index
?plot index
?data-file index
?datafile index
?index
 The `index` keyword allows only some of the data sets in a multi-data-set
 file to be plotted.

 Syntax:
       plot 'file' index <m>{{:<n>}:<p>}

 Data sets are separated by pairs of blank records.  `index <m>` selects only
 set <m>; `index <m>:<n>` selects sets in the range <m> to <n>; and `index
 <m>:<n>:<p>` selects indices <m>, <m>+<p>, <m>+2<p>, etc., but stopping at
 <n>.  Following C indexing, the index 0 is assigned to the first data set in
 the file.  Specifying too large an index results in an error message.  If
 `index` is not specified, all sets are plotted as a single data set.

 Example:
       plot 'file' index 4:5
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/multimsh.html"> splot with indices demo. </a>
4 smooth
?commands plot datafile smooth
?plot datafile smooth
?plot smooth
?data-file smooth
?datafile smooth
?smooth
 `gnuplot` includes a few general-purpose routines for interpolation and
 approximation of data; these are grouped under the `smooth` option.  More
 sophisticated data processing may be performed by preprocessing the data
 externally or by using `fit` with an appropriate model.

 Syntax:
       smooth {unique | csplines | acsplines | bezier | sbezier}

 `unique` plots the data after making them monotonic.  Each of the other
 routines uses the data to determine the coefficients of a continuous curve
 between the endpoints of the data.  This curve is then plotted in the same
 manner as a function, that is, by finding its value at uniform intervals
 along the abscissa (see `set samples`) and connecting these points with
 straight line segments (if a line style is chosen).

 If `autoscale` is in effect, the ranges will be computed such that the
 plotted curve lies within the borders of the graph.

 If too few points are available to allow the selected option to be applied,
 an error message is produced.  The minimum number is one for `unique`, four
 for `acsplines`, and three for the others.

 The `smooth` options have no effect on function plots.
5 acsplines
?commands plot datafile smooth acsplines
?plot datafile smooth acsplines
?data-file smooth acsplines
?datafile smooth acsplines
?plot smooth acsplines
?plot acsplines
?smooth acsplines
?acsplines
 The `acsplines` option approximates the data with a "natural smoothing spline".
 After the data are made monotonic in x (see `smooth unique`), a curve is
 piecewise constructed from segments of cubic polynomials whose coefficients
 are found by the weighting the data points; the weights are taken from the
 third column in the data file.  That default can be modified by the third
 entry in the `using` list, e.g.,
       plot 'data-file' using 1:2:(1.0) smooth acsplines

 Qualitatively, the absolute magnitude of the weights determines the number
 of segments used to construct the curve.  If the weights are large, the
 effect of each datum is large and the curve approaches that produced by
 connecting consecutive points with natural cubic splines.  If the weights are
 small, the curve is composed of fewer segments and thus is smoother; the
 limiting case is the single segment produced by a weighted linear least
 squares fit to all the data.  The smoothing weight can be expressed in terms
 of errors as a statistical weight for a point divided by a "smoothing factor"
 for the curve so that (standard) errors in the file can be used as smoothing
 weights.

 Example:
       sw(x,S)=1/(x*x*S)
       plot 'data_file' using 1:2:(sw($3,100)) smooth acsplines
5 bezier
?commands plot datafile smooth bezier
?plot datafile smooth bezier
?plot smooth bezier
?data-file smooth bezier
?datafile smooth bezier
?plot bezier
?smooth bezier
?bezier
 The `bezier` option approximates the data with a Bezier curve of degree n
 (the number of data points) that connects the endpoints.
5 csplines
?commands plot datafile smooth csplines
?plot datafile smooth csplines
?plot smooth csplines
?data-file smooth csplines
?datafile smooth csplines
?plot csplines
?smooth csplines
?csplines
 The `csplines` option connects consecutive points by natural cubic splines
 after rendering the data monotonic (see `smooth unique`).
5 sbezier
?commands plot datafile smooth sbezier
?plot datafile smooth sbezier
?plot smooth sbezier
?data-file smooth sbezier
?datafile smooth sbezier
?plot sbezier
?smooth sbezier
?sbezier
 The `sbezier` option first renders the data monotonic (`unique`) and then
 applies the `bezier` algorithm.
5 unique
?commands plot datafile smooth unique
?plot datafile smooth unique
?plot smooth unique
?data-file smooth unique
?datafile smooth unique
?plot unique
?smooth unique
?unique
 The `unique` option makes the data monotonic in x; points with the same
 x-value are replaced by a single point having the average y-value.  The
 resulting points are then connected by straight line segments.
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/mgr.html"> See demos. </a>
4 special-filenames
?commands plot datafile special-filenames
?plot datafile special-filenames
?plot special-filenames
?datafile special-filenames
?special-filenames
 A special filename of `'-'` specifies that the data are inline; i.e., they
 follow the command.  Only the data follow the command; `plot` options like
 filters, titles, and line styles remain on the 'plot' command line.  This is
 similar to << in unix shell script, and $DECK in VMS DCL.  The data are
 entered as though they are being read from a file, one data point per record.
 The letter "e" at the start of the first column terminates data entry.  The
 `using` option can be applied to these data---using it to filter them through
 a function might make sense, but selecting columns probably doesn't!

 `'-'` is intended for situations where it is useful to have data and commands
 together, e.g., when `gnuplot` is run as a sub-process of some front-end
 application.  Some of the demos, for example, might use this feature.  While
 `plot` options such as `index` and `every` are recognized, their use forces
 you to enter data that won't be used.  For example, while

       plot '-' index 0, '-' index 1
       2
       4
       6


       10
       12
       14
       e
       2
       4
       6


       10
       12
       14
       e

 does indeed work,

       plot '-', '-'
       2
       4
       6
       e
       10
       12
       14
       e

 is a lot easier to type.

 If you use `'-'` with `replot`, you may need to enter the data more than once
 (see `replot`).

 A blank filename ('') specifies that the previous filename should be reused.
 This can be useful with things like

       plot 'a/very/long/filename' using 1:2, '' using 1:3, '' using 1:4

 (If you use both `'-'` and `''` on the same `plot` command, you'll need to
 have two sets of inline data, as in the example above.)

 On some computer systems with a popen function (Unix), the datafile can be
 piped through a shell command by starting the file name with a '<'.  For
 example,

       pop(x) = 103*exp(-x/10)
       plot "< awk '{print $1-1965, $2}' population.dat", pop(x)

 would plot the same information as the first population example but with
 years since 1965 as the x axis.  If you want to execute this example, you
 have to delete all comments from the data file above or substitute the
 following command for the first part of the command above (the part up to
 the comma):

       plot "< awk '$0 !~ /^#/ {print $1-1965, $2}' population.dat"

 While this approach is most flexible, it is possible to achieve simple
 filtering with the `using` or `thru` keywords.
4 thru
?commands plot datafile thru
?plot datafile thru
?plot thru
?data-file thru
?datafile thru
?thru
 The `thru` function is provided for backward compatibility.

 Syntax:
       plot 'file' thru f(x)

 It is equivalent to:

       plot 'file' using 1:(f($2))

 While the latter appears more complex, it is much more flexible.  The more
 natural

       plot 'file' thru f(y)

 also works (i.e. you can use y as the dummy variable).

 `thru` is parsed for `splot` and `fit` but has no effect.
4 using
?commands plot datafile using
?plot datafile using
?plot using
?data-file using
?datafile using
?using
 The most common datafile modifier is `using`.

 Syntax:
       plot 'file' using {<entry> {:<entry> {:<entry> ...}}} {'format'}

 If a format is specified, each datafile record is read using the C library's
 'scanf' function, with the specified format string.  Otherwise the record is
 read and broken into columns at spaces or tabs.  A format cannot be specified
 if time-format data is being used (this must be done by `set data time`).

 The resulting array of data is then sorted into columns according to the
 entries.  Each <entry> may be a simple column number, which selects the
 datum, an expression enclosed in parentheses, or empty.  The expression can
 use $1 to access the first item read, $2 for the second item, and so on.  It
 can also use `column(x)` and `valid(x)` where x is an arbitrary expression
 resulting in an integer.  `column(x)` returns the x'th datum; `valid(x)`
 tests that the datum in the x'th column is a valid number.  A column number
 of 0 generates a number increasing (from zero) with each point, and is reset
 upon encountering two blank records.  A column number of -1 gives the
 dataline number, which starts at 0, increments at single blank records, and
 is reset at double blank records.  A column number of -2 gives the index
 number, which is incremented only when two blank records are found.  An empty
 <entry> will default to its order in the list of entries.  For example,
 `using ::4` is interpreted as `using 1:2:4`.

 N.B.---the `call` command also uses $'s as a special character.  See `call`
 for details about how to include a column number in a `call` argument list.

 If the `using` list has but a single entry, that <entry> will be used for y
 and the data point number is used for x; for example, "`plot 'file' using 1`"
 is identical to "`plot 'file' using 0:1`".  If the `using` list has two
 entries, these will be used for x and y.  Additional entries are usually
 errors in x and/or y.  See `set style` for details about plotting styles that
 make use of error information, and `fit` for use of error information in
 curve fitting.

 'scanf' accepts several numerical specifications but `gnuplot` requires all
 inputs to be double-precision floating-point variables, so `lf` is the only
 permissible specifier.  'scanf' expects to see white space---a blank, tab
 ("\t"), newline ("\n"), or formfeed ("\f")---between numbers; anything else
 in the input stream must be explicitly skipped.

 Note that the use of "\t", "\n", or "\f" or requires use of double-quotes
 rather than single-quotes.

 Examples:

 This creates a plot of the sum of the 2nd and 3rd data against the first:
 (The format string specifies comma- rather than space-separated columns.)
       plot 'file' using 1:($2+$3) '%lf,%lf,%lf'

 In this example the data are read from the file "MyData" using a more
 complicated format:
       plot 'MyData' using "%*lf%lf%*20[^\n]%lf"

 The meaning of this format is:

       %*lf        ignore a number
       %lf         read a double-precision number (x by default)
       %*20[^\n]   ignore 20 non-newline characters
       %lf         read a double-precision number (y by default)

 One trick is to use the ternary `?:` operator to filter data:

       plot 'file' using 1:($3>10 ? $2 : 1/0)

 which plots the datum in column two against that in column one provided
 the datum in column three exceeds ten.  `1/0` is undefined; `gnuplot`
 quietly ignores undefined points, so unsuitable points are suppressed.

 In fact, you can use a constant expression for the column number, provided it
 doesn't start with an opening parenthesis; constructs like `using
 0+(complicated expression)` can be used.  The crucial point is that the
 expression is evaluated once if it doesn't start with a left parenthesis, or
 once for each data point read if it does.

 If timeseries data are being used, the time can span multiple columns.  The
 starting column should be specified.  Note that the spaces within the time
 must be included when calculating starting columns for other data.  E.g., if
 the first element on a line is a time with an embedded space, the y value
 should be specified as column three.

 It should be noted that `plot 'file'`, `plot 'file' using 1:2`, and `plot
 'file' using ($1):($2)` can be subtly different: 1) if `file` has some lines
 with one column and some with two, the first will invent x values when they
 are missing, the second will quietly ignore the lines with one column, and
 the third will store an undefined value for lines with one point (so that in
 a plot with lines, no line joins points across the bad point); 2) if a line
 contains text at the first column, the first will abort the plot on an error,
 but the second and third should quietly skip the garbage.

 In fact, it is often possible to plot a file with lots of lines of garbage at
 the top simply by specifying

       plot 'file' using 1:2

 However, if you want to leave text in your data files, it is safer to put the
 comment character (#) in the first column of the text lines.
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/using.html"> Feeble using demos. </a>
3 errorbars
?commands plot errorbars
?commands splot errorbars
?plot errorbars
?splot errorbars
?errorbars
 Error bars are supported for 2-d data file plots by reading one to four
 additional columns (or `using` entries); these additional values are used in
 different ways by the various errorbar styles.

 In the default situation, `gnuplot` expects to see three, four, or six
 numbers on each line of the data file---either

       (x, y, ydelta),
       (x, y, ylow, yhigh),
       (x, y, xdelta),
       (x, y, xlow, xhigh),
       (x, y, xdelta, ydelta), or
       (x, y, xlow, xhigh, ylow, yhigh).

 The x coordinate must be specified.  The order of the numbers must be
 exactly as given above, though the `using` qualifier can manipulate the order
 and provide values for missing columns.  For example,

       plot 'file' with errorbars
       plot 'file' using 1:2:(sqrt($1)) with xerrorbars
       plot 'file' using 1:2:($1-$3):($1+$3):4:5 with xyerrorbars

 The last example is for a file containing an unsupported combination of
 relative x and absolute y errors.  The `using` entry generates absolute x min
 and max from the relative error.

 The y error bar is a vertical line plotted from (x, ylow) to (x, yhigh).
 If ydelta is specified instead of ylow and yhigh, ylow = y - ydelta and
 yhigh = y + ydelta are derived.  If there are only two numbers on the record,
 yhigh and ylow are both set to y.  The x error bar is a horizontal line
 computed in the same fashion.  To get lines plotted between the data points,
 `plot` the data file twice, once with errorbars and once with lines (but
 remember to use the `notitle` option on one to avoid two entries in the key).

 The error bars have crossbars at each end unless `set bar` is used (see `set
 bar` for details).

 If autoscaling is on, the ranges will be adjusted to include the error bars.
^ <a href="http://www.nas.nasa.gov/~woo/gnuplot/errorbar/errorbar.html"> Errorbar demos. </a>

 See `plot using`, `plot with`, and `set style` for more information.
3 parametric
?commands plot parametric
?commands splot parametric
?plot parametric
?splot parametric
?parametric
 When in parametric mode (`set parametric`) mathematical expressions must be
 given in pairs for `plot` and in triplets for `splot`.

 Examples:
       plot sin(t),t**2
       splot cos(u)*cos(v),cos(u)*sin(v),sin(u)

 Data files are plotted as before, except any preceding parametric function
 must be fully specified before a data file is given as a plot.  In other
 words, the x parametric function (`sin(t)` above) and the y parametric
 function (`t**2` above) must not be interrupted with any modifiers or data
 functions; doing so will generate a syntax error stating that the parametric
 function is not fully specified.

 Other modifiers, such as `with` and `title`, may be specified only after the
 parametric function has been completed:

       plot sin(t),t**2 title 'Parametric example' with linespoints
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/param.html"> Parametric Mode Demos. </a>
3 ranges
?commands plot ranges
?commands splot ranges
?plot ranges
?splot ranges
?ranges
 The optional ranges specify the region of the graph that will be displayed.

 Syntax:
       [{<dummy-var>=}{{<min>}:{<max>}}]
       [{{<min>}:{<max>}}]

 The first form applies to the independent variable (`xrange` or `trange`, if
 in parametric mode).  The second form applies to the dependent variable
 `yrange` (and `xrange`, too, if in parametric mode).  <dummy-var> is a new
 name for the independent variable.  (The defaults may be changed with `set
 dummy`.)  The optional <min> and <max> terms can be constant expressions or *.

 In non-parametric mode, the order in which ranges must be given is `xrange`
 and `yrange`.

 In parametric mode, the order for the `plot` command is `trange`, `xrange`,
 and `yrange`.  The following `plot` command shows setting the `trange` to
 [-pi:pi], the `xrange` to [-1.3:1.3] and the `yrange` to [-1:1] for the
 duration of the graph:

       plot [-pi:pi] [-1.3:1.3] [-1:1] sin(t),t**2

 Note that the x2range and y2range cannot be specified here---`set x2range`
 and `set y2range` must be used.

 Ranges are interpreted in the order listed above for the appropriate mode.
 Once all those needed are specified, no further ones must be listed, but
 unneeded ones cannot be skipped---use an empty range `[]` as a placeholder.

 `*` can be used to allow autoscaling of either of min and max.  See also
 `set autoscale`.

 Ranges specified on the `plot` or `splot` command line affect only that
 graph; use the `set xrange`, `set yrange`, etc., commands to change the
 default ranges for future graphs.

 With time data, you must provide the range (in the same manner as the time
 appears in the datafile) within quotes.  `gnuplot` uses the `timefmt` string
 to read the value---see `set timefmt`.

 Examples:

 This uses the current ranges:
       plot cos(x)

 This sets the x range only:
       plot [-10:30] sin(pi*x)/(pi*x)

 This is the same, but uses t as the dummy-variable:
       plot [t = -10 :30]  sin(pi*t)/(pi*t)

 This sets both the x and y ranges:
       plot [-pi:pi] [-3:3]  tan(x), 1/x

 This sets only the y range, and turns off autoscaling on both axes:
       plot [ ] [-2:sin(5)*-8] sin(x)**besj0(x)

 This sets xmax and ymin only:
       plot [:200] [-pi:]  exp(sin(x))

 This sets the x range for a timeseries:
       set timefmt "%d/%m/%y %H:%M"
       plot ["1/6/93 12:00":"5/6/93 12:00"] 'timedata.dat'

^<a href="http://www.nas.nasa.gov/~woo/gnuplot/ranges/ranges.html"> See Demo. </a>
3 title
?commands plot title
?commands splot title
?plot title
?splot title
 A line title for each function and data set appears in the key, accompanied
 by a sample of the line and/or symbol used to represent it.  It can be
 changed by using the `title` option.

 Syntax:
       title "<title>" | notitle

 where <title> is the new title of the line and must be enclosed in quotes.
 The quotes will not be shown in the key.  A special character may be given as
 a backslash followed by its octal value ("\345").  The tab character "\t" is
 understood.  Note that backslash processing occurs only for strings enclosed
 in double quotes---use single quotes to prevent such processing.  The newline
 character "\n" is not processed in key entries in either type of string.

 The line title and sample can be omitted from the key by using the keyword
 `notitle`.  A null title (`title ''`) is equivalent to `notitle`.  If only
 the sample is wanted, use one or more blanks (`title ' '`).

 By default the line title is the function or file name as it appears on the
 `plot` command.  If it is a file name, any datafile modifiers specified will
 be included in the default title.

 The layout of the key itself (position, title justification, etc.) can be
 controlled by `set key`.  Please see `set key` for details.

 Examples:

 This plots y=x with the title 'x':
       plot x

 This plots x squared with title "x^2" and file "data.1" with title
 "measured data":
       plot x**2 title "x^2", 'data.1' t "measured data"

 This puts an untitled circular border around a polar graph:
       set polar; plot my_function(t), 1 notitle
3 with
?commands plot with
?commands splot with
?commands plot style
?commands splot style
?plot with
?plot style
?splot with
?splot style
?style
?with
 Functions and data may be displayed in one of a large number of styles.
 The `with` keyword provides the means of selection.

 Syntax:
       with <style> { {linestyle | ls <line_style>}
                      | {{linetype | lt <line_type>}
                         {linewidth | lw <line_width>}
                         {pointtype | pt <point_type>}
                         {pointsize | ps <point_size>}} }

 where <style> is either `lines`, `points`, `linespoints`, `impulses`, `dots`,
 `steps`, `fsteps`, `histeps`, `errorbars`, `xerrorbars`, `yerrorbars`,
 `xyerrorbars`, `boxes`, `boxerrorbars`, `boxxyerrorbars`, `financebars`,
 `candlesticks` or `vector`.  Some of these styles require additional
 information.  See `set style <style>` for details of each style.

 Default styles are chosen with the `set function style` and `set data style`
 commands.

 By default, each function and data file will use a different line type and
 point type, up to the maximum number of available types.  All terminal
 drivers support at least six different point types, and re-use them, in
 order, if more are required.  The LaTeX driver supplies an additional six
 point types (all variants of a circle), and thus will only repeat after 12
 curves are plotted with points.  The PostScript drivers (`postscript`)
 supplies a total of 64.

 If you wish to choose the line or point type for a single plot, <line_type>
 and <point_type> may be specified.  These are positive integer constants (or
 expressions) that specify the line type and point type to be used for the
 plot.  Use `test` to display the types available for your terminal.

 You may also scale the line width and point size for a plot by using
 <line_width> and <point_size>, which are specified relative to the default
 values for each terminal.  The pointsize may also be altered globally---see
 `set pointsize` for details.  But note that both <point_size> as set here and
 as set by `set pointsize` multiply the default point size---their effects are
 not cumulative.  That is, `set pointsize 2; plot x w p ps 3` will use points
 three times default size, not six.

 If you have defined specific line type/width and point type/size combinations
 with `set linestyle`, one of these may be selected by setting <line_style> to
 the index of the desired style.

 The keywords may be abbreviated as indicated.

 Note that the `linewidth` and `pointsize` options are not supported by all
 terminals.

 Examples:

 This plots sin(x) with impulses:
       plot sin(x) with impulses

 This plots x with points, x**2 with the default:
       plot x*y w points, x**2 + y**2

 This plots tan(x) with the default function style, file "data.1" with lines:
       plot [ ] [-2:5] tan(x), 'data.1' with l

 This plots "leastsq.dat" with impulses:
       plot 'leastsq.dat' w i

 This plots the data file "population" with boxes:
       plot 'population' with boxes

 This plots "exper.dat" with errorbars and lines connecting the points
 (errorbars require three or four columns):
       plot 'exper.dat' w lines, 'exper.dat' notitle w errorbars

 This plots sin(x) and cos(x) with linespoints, using the same line type but
 different point types:
       plot sin(x) with linesp lt 1 pt 3, cos(x) with linesp lt 1 pt 4

 This plots file "data" with points of type 3 and twice usual size:
       plot 'data' with points pointtype 3 pointsize 2

 This plots two data sets with lines differing only by weight:
       plot 'd1' t "good" w l lt 2 lw 3, 'd2' t "bad" w l lt 2 lw 1

 See `set style` to change the default styles.
^ <a href="http://www.nas.nasa.gov/~woo/gnuplot/styles/styles.html"> Styles demos. </a>
2 print
?commands print
?print
 The `print` command prints the value of <expression> to the screen.  It is
 synonymous with `pause 0`.  <expression> may be anything that `gnuplot` can
 evaluate that produces a number, or it can be a string.

 Syntax:
       print <expression> {, <expression>, ...}

 See `expressions`.
2 pwd
?commands pwd
?pwd
 The `pwd` command prints the name of the working directory to the screen.
2 quit
?commands quit
?quit
 The `exit` and `quit` commands and END-OF-FILE character will exit `gnuplot`.
 Each of these commands will clear the output device (as does the `clear`
 command) before exiting.
2 replot
?commands replot
?replot
 The `replot` command without arguments repeats the last `plot` or `splot`
 command.  This can be useful for viewing a plot with different `set` options,
 or when generating the same plot for several devices.

 Arguments specified after a `replot` command will be added onto the last
 `plot` or `splot` command (with an implied ',' separator) before it is
 repeated.  `replot` accepts the same arguments as the `plot` and `splot`
 commands except that ranges cannot be specified.  Thus you can use `replot`
 to plot a function against the second axes if the previous command was `plot`
 but not if it was `splot`, and similarly you can use `replot` to add a plot
 from a binary file only if the previous command was `splot`.

 N.B.---use of

       plot '-' ; ... ; replot

 is not recommended.  `gnuplot` does not store the inline data internally, so
 since `replot` appends new information to the previous `plot` and then
 executes the modified command, the `'-'` from the initial `plot` will expect
 to read inline data again.

 Note that `replot` does not work in `multiplot` mode, since it reproduces
 only the last plot rather than the entire screen.

 See also `command-line-editing` for ways to edit the last `plot` (`splot`)
 command.
2 reread
?commands reread
?reread
 The `reread` command causes the current `gnuplot` command file, as specified
 by a `load` command or on the command line, to be reset to its starting
 point before further commands are read from it.  This essentially implements
 an endless loop of the commands from the beginning of the command file to
 the `reread` command.  (But this is not necessarily a disaster---`reread` can
 be very useful when used in conjunction with `if`.  See `if` for details.)
 The `reread` command has no effect if input from standard input.

 Examples:

 Suppose the file "looper" contains the commands
       a=a+1
       plot sin(x*a)
       pause -1
       if(a<5) reread
 and from within `gnuplot` you submit the commands
       a=0
       load 'looper'
 The result will be four plots (separated by the `pause` message).

 Suppose the file "data" contains six columns of numbers with a total yrange
 from 0 to 10; the first is x and the next are five different functions of x.
 Suppose also that the file "plotter" contains the commands
       c_p = c_p+1
       plot "$0" using 1:c_p with lines linetype c_p
       if(c_p <  n_p) reread
 and from within `gnuplot` you submit the commands
       n_p=6
       c_p=1
       set nokey
       set yrange [0:10]
       set multiplot
       call 'plotter' 'data'
       set nomultiplot
 The result is a single graph consisting of five plots.  The yrange must be
 set explicitly to guarantee that the five separate graphs (drawn on top of
 each other in multiplot mode) will have exactly the same axes.  The linetype
 must be specified; otherwise all the plots would be drawn with the same type.
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/animate.html"> Reread Animation Demo</a>
2 reset
?commands reset
?reset
 The `reset` command causes all options that can be set with the `set`
 command to take on their default values.  The only exceptions are that the
 terminal set with `set term` and the output file set with `set output` are
 left unchanged.  This command is useful, e.g., to restore the default
 settings at the end of a command file, or to return to a defined state after
 lots of settings have been changed within a command file.  Please refer to
 the `set` command to see the default values that the various options take.
2 save
?commands save
?save
 The `save` command saves user-defined functions, variables, `set` options,
 or all three, plus the last `plot` (`splot`) command to the specified file.

 Syntax:
       save  {<option>} '<filename>'

 where <option> is `functions`, `variables` or `set`. If no option is used,
 `gnuplot` saves functions, variables, `set` options and the last `plot`
 (`splot`) command.

 `save`d files are written in text format and may be read by the `load`
 command.

 The filename must be enclosed in quotes.

 Examples:
       save 'work.gnu'
       save functions 'func.dat'
       save var 'var.dat'
       save set 'options.dat'
2 set-show
?commands set
?commands show
?set
?show
?show all
 The `set` command can be used to sets _lots_ of options.  No screen is
 drawn, however, until a `plot`, `splot`, or `replot` command is given.

 The `show` command shows their settings;  `show all` shows all the
 settings.

 If a variable contains time/date data, `show` will display it according to
 the format currently defined by `set timefmt`, even if that was not in effect
 when the variable was initially defined.
3 angles
?commands set angles
?commands show angles
?set angles
?show angles
?angles
?commands set angles degrees
?set angles degrees
?angles degrees
?degrees
 By default, `gnuplot` assumes the independent variable in polar graphs is in
 units of radians.  If `set angles degrees` is specified before `set polar`,
 then the default range is [0:360] and the independent variable has units of
 degrees.  This is particularly useful for plots of data files.  The angle
 setting also applies to 3-d mapping as set via the `set mapping` command.

 Syntax:
       set angles {degrees | radians}
       show angles

 The angle specified in `set grid polar` is also read and displayed in the
 units specified by `set angles`.

 `set angles` also affects the arguments of the machine-defined functions
 sin(x), cos(x) and tan(x), and the outputs of asin(x), acos(x), atan(x),
 atan2(x), and arg(x).  It has no effect on the arguments of hyperbolic
 functions or Bessel functions.  However, the output arguments of inverse
 hyperbolic functions of complex arguments are affected; if these functions
 are used, `set angles radians` must be in effect to maintain consistency
 between input and output arguments.

       x={1.0,0.1}
       set angles radians
       y=sinh(x)
       print y         #prints {1.16933, 0.154051}
       print asinh(y)  #prints {1.0, 0.1}
 but
       set angles degrees
       y=sinh(x)
       print y         #prints {1.16933, 0.154051}
       print asinh(y)  #prints {57.29578, 5.729578}
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/poldat.html"> Polar plot using `set angles`. </a>
3 arrow
?commands set arrow
?commands set noarrow
?commands show arrow
?set arrow
?set noarrow
?show arrow
?arrow
?noarrow
 Arbitrary arrows can be placed on a plot using the `set arrow` command.

 Syntax:
       set arrow {<tag>} {from <position>} {to <position>} {{no}head}
                 { {linestyle | ls <line_style>}
                   | {linetype | lt <line_type>}
                     {linewidth | lw <line_width} }
       set noarrow {<tag>}
       show arrow

 <tag> is an integer that identifies the arrow.  If no tag is given, the
 lowest unused tag value is assigned automatically.  The tag can be used to
 delete or change a specific arrow.  To change any attribute of an existing
 arrow, use the `set arrow` command with the appropriate tag and specify the
 parts of the arrow to be changed.

 The <position>s are specified by either x,y or x,y,z, and may be preceded by
 `first`, `second`, `graph`, or `screen` to select the coordinate system.
 Unspecified coordinates default to 0.  The endpoints can be specified in
 one of four coordinate systems---`first` or `second` axes, `graph` or
 `screen`.  See `coordinates` for details.  A coordinate system specifier
 does not carry over from the "from" position to the "to" position.  Arrows
 outside the screen boundaries are permitted but may cause device errors.

 Specifying `nohead` produces an arrow drawn without a head---a line segment.
 This gives you yet another way to draw a line segment on the plot.  By
 default, arrows have heads.

 The line style may be selected from a user-defined list of line styles (see
 `set linestyle`) or may be defined here by providing values for <line_type>
 (an index from the default list of styles) and/or <line_width> (which is a
 multiplier for the default width).

 Note, however, that if a user-defined line style has been selected, its
 properties (type and width) cannot be altered merely by issuing another
 `set arrow` command with the appropriate index and `lt` or `lw`.

 Examples:

 To set an arrow pointing from the origin to (1,2) with user-defined style 5,
 use:
       set arrow to 1,2 ls 5

 To set an arrow from bottom left of plotting area to (-5,5,3), and tag the
 arrow number 3, use:
       set arrow 3 from graph 0,0 to -5,5,3

 To change the preceding arrow to end at 1,1,1, without an arrow head and
 double its width, use:
       set arrow 3 to 1,1,1 nohead lw 2

 To draw a vertical line from the bottom to the top of the graph at x=3, use:
       set arrow from 3, graph 0 to 3, graph 1 nohead

 To delete arrow number 2, use:
       set noarrow 2

 To delete all arrows, use:
       set noarrow

 To show all arrows (in tag order), use:
       show arrow
^ <a href="http://www.nas.nasa.gov/~woo/gnuplot/arrows/arrows.html"> Arrows Demos. </a>
3 autoscale
?commands set autoscale
?commands set noautoscale
?commands show autoscale
?set autoscale
?set noautoscale
?show autoscale
?autoscale
?noautoscale
 Autoscaling may be set individually on the x, y or z axis or globally on all
 axes. The default is to autoscale all axes.

 Syntax:
       set autoscale {<axes>{min|max}}
       set noautoscale {<axes>{min|max}}
       show autoscale

 where <axes> is either `x`, `y`, `z`, `x2`, `y2` or `xy`.  A keyword with
 `min` or `max` appended (this cannot be done with `xy`) tells `gnuplot` to
 autoscale just the minimum or maximum of that axis.  If no keyword is given,
 all axes are autoscaled.

 When autoscaling, the axis range is automatically computed and the dependent
 axis (y for a `plot` and z for `splot`) is scaled to include the range of the
 function or data being plotted.

 If autoscaling of the dependent axis (y or z) is not set, the current y or z
 range is used.

 Autoscaling the independent variables (x for `plot` and x,y for `splot`) is a
 request to set the domain to match any data file being plotted.  If there are
 no data files, autoscaling an independent variable has no effect.  In other
 words, in the absence of a data file, functions alone do not affect the x
 range (or the y range if plotting z = f(x,y)).

 Please see `set xrange` for additional information about ranges.

 The behavior of autoscaling remains consistent in parametric mode, (see `set
 parametric`).  However, there are more dependent variables and hence more
 control over x, y, and z axis scales.  In parametric mode, the independent or
 dummy variable is t for `plot`s and u,v for `splot`s.  `autoscale` in
 parametric mode, then, controls all ranges (t, u, v, x, y, and z) and allows
 x, y, and z to be fully autoscaled.

 Autoscaling works the same way for polar mode as it does for parametric mode
 for `plot`, with the extension that in polar mode `set dummy` can be used to
 change the independent variable from t (see `set dummy`).

 When tics are displayed on second axes but no plot has been specified for
 those axes, x2range and y2range are inherited from xrange and yrange.  This
 is done _before_ xrange and yrange are autoextended to a whole number of
 tics, which can cause unexpected results.

 Examples:

 This sets autoscaling of the y axis (other axes are not affected):
       set autoscale y

 This sets autoscaling only for the minimum of the y axis (the maximum of the
 y axis and the other axes are not affected):
       set autoscale ymin

 This sets autoscaling of the x and y axes:
       set autoscale xy

 This sets autoscaling of the x, y, z, x2 and y2 axes:
       set autoscale

 This disables autoscaling of the x, y, z, x2 and y2 axes:
       set noautoscale

 This disables autoscaling of the z axis only:
       set noautoscale z
4 parametric mode
?commands set autoscale parametric
?set autoscale parametric
?set autoscale t
 When in parametric mode (`set parametric`), the xrange is as fully scalable
 as the y range.  In other words, in parametric mode the x axis can be
 automatically scaled to fit the range of the parametric function that is
 being plotted.  Of course, the y axis can also be automatically scaled just
 as in the non-parametric case.  If autoscaling on the x axis is not set, the
 current x range is used.

 Data files are plotted the same in parametric and non-parametric mode.
 However, there is a difference in mixed function and data plots: in
 non-parametric mode with autoscaled x, the x range of the datafile controls
 the x range of the functions; in parametric mode it has no influence.

 For completeness a last command `set autoscale t` is accepted.  However, the
 effect of this "scaling" is very minor.  When `gnuplot` determines that the
 t range would be empty, it makes a small adjustment if autoscaling is true.
 Otherwise, `gnuplot` gives an error.  Such behavior may, in fact, not be very
 useful and the command `set autoscale t` is certainly questionable.

 `splot` extends the above ideas as you would expect.  If autoscaling is set,
 then x, y, and z ranges are computed and each axis scaled to fit the
 resulting data.
4 polar mode
?commands set autoscale polar
?set autoscale polar
?set autoscale t
 When in polar mode (`set polar`), the xrange and the yrange are both found
 from the polar coordinates, and thus they can both be automatically scaled.
 In other words, in polar mode both the x and y axes can be automatically
 scaled to fit the ranges of the polar function that is being plotted.

 When plotting functions in polar mode, the rrange may be autoscaled.  When
 plotting data files in polar mode, the trange may also be autoscaled.  Note
 that if the trange is contained within one quadrant, autoscaling will produce
 a polar plot of only that single quadrant.

 Explicitly setting one or two ranges but not others may lead to unexpected
 results.
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/poldat.html"> See polar demos </a>
3 bar
?commands set bar
?commands show bar
?set bar
?show bar
 The `set bar` command controls the tics at the ends of errorbars.

 Syntax:
       set bar {small | large | <size>}
       show bar

 `small` is a synonym for 0.0, and `large` for 1.0.
 The default is 1.0 if no size is given.
3 bmargin
?commands set bmargin
?set bmargin
?bmargin
 The command `set bmargin` sets the size of the bottom margin.  Please see
 `set margin` for details.
3 border
?commands set border
?commands set noborder
?commands show border
?set border
?set noborder
?show border
?border
?noborder
 The `set border` and `set noborder` commands control the display of the graph
 borders for the `plot` and `splot` commands.

 Syntax:
       set border {<integer> { {linestyle | ls <line_style>}
                               | {linetype | lt <line_type> }
                                 {linewidth | lw <line_width>} } }
       set noborder
       show border

 The borders are encoded in a 12-bit integer: the bottom four bits control the
 border for `plot` and the sides of the base for `splot`; The next four bits
 control the verticals in `splot`; the top four bits control the edges on top
 of the `splot`.  In detail, the `<integer>` should be the sum of the
 appropriate entries from the following table:

@start table - first is interactive cleartext form
                         plot border     splot         splot
           Side          splot base    verticals        top
       bottom (south)         1            16           256
       left   (west)          2            32           512
       top    (north)         4            64          1024
       right  (east)          8           128          2048
#\begin{tabular}{|cc|ccc|} \hline
#\multicolumn{5}{|c|}{Graph Border Encoding} \\ \hline \hline
# & & \multicolumn{3}{|c|}{Integer value of selection bit} \\ \cline{3-5}
# & & plot border & splot & splot \\
#\multicolumn{2}{|c|}{Side}& splot base & verticals & top \\ \hline
#bottom & (south) & 1 & 16 & 256 \\
#left   & (west)  & 2 & 32 & 512 \\
#top    & (north) & 4 & 64 & 1024 \\
#right  & (east)  & 8 & 128 & 2048 \\
%c c c c c .
%@plot border@splot@splot
%@splot base@verticals@top
%_
%bottom (south)@1@16@256
%left   (west)@2@32@512
%top    (north)@4@64@1024
%right  (east)@8@128@2048
@end table

 The default is 31, which is all four sides for `plot`, and base and z axis
 for `splot`.

 Using the optional <line_style>, <line_type> and <line_width>
 specifiers, the way the border lines are drawn can be influenced
 (limited by what the current terminal driver supports).  By default,
 the border is drawn with twice the usual linewidth.  The <line_width>
 specifier scales this default value; for example, `set border 15 lw 2`
 will produce a border with four times the usual linewidth.

 Various axes or combinations of axes may be added together in the command.

 To have tics on edges other than bottom and left, disable the usual tics and
 enable the second axes.

 Examples:

 Draw all borders:
       set border

 Draw only the SOUTHWEST borders:
       set border 3

 Draw a complete box around a `splot`:
       set border 4095

 Draw a partial box, omitting the front vertical:
       set border 127+256+512

 Draw only the NORTHEAST borders:
       set noxtics; set noytics; set x2tics; set y2tics; set border 12

^ <a href="http://www.nas.nasa.gov/~woo/gnuplot/borders/borders.html"> Borders Demo. </a>
3 boxwidth
?commands set boxwidth
?commands show boxwidth
?set boxwidth
?show boxwidth
?boxwidth
 The `set boxwidth` command is used to set the default width of boxes in the
 `boxes` and `boxerrorbars` styles.

 Syntax:
       set boxwidth {<width>}
       show boxwidth

 If a data file is plotted without the width being specified in the third,
 fourth, or fifth column (or `using` entry), or if a function is plotted, the
 width of each box is set by the `set boxwidth` command.  (If a width is given
 both in the file and by the `set boxwidth` command, the one in the file is
 used.)  If the width is not specified in one of these ways, the width of each
 box will be calculated automatically so that it touches the adjacent boxes.
 In a four-column data set, the fourth column will be interpreted as the box
 width unless the width is set to -2.0, in which case the width will be
 calculated automatically.  See `set style boxerrorbars` for more details.

 To set the box width to automatic use the command
       set boxwidth
 or, for four-column data,
       set boxwidth -2

 The same effect can be achieved with the `using` keyword in `plot`:
       plot 'file' using 1:2:3:4:(-2)
3 clabel
?commands set clabel
?commands set noclabel
?commands show clabel
?set clabel
?set noclabel
?show clabel
?clabel
?noclabel
 `gnuplot` will vary the linetype used for each contour level when clabel is
 set.  When this option on (the default), a legend labels each linestyle with
 the z level it represents.  It is not possible at present to separate the
 contour labels from the surface key.

 Syntax:
       set clabel {'<format>'}
       set noclabel
       show clabel

 The default for the format string is %8.3g, which gives three decimal places.
 This may produce poor label alignment if the key is altered from its default
 configuration.

 The first contour linetype, or only contour linetype when clabel is off, is
 the surface linetype +1; contour points are the same style as surface points.

 See also `set contour`.
3 clip
?commands set clip
?commands set noclip
?commands show clip
?set clip
?set noclip
?show clip
?clip
?noclip
 `gnuplot` can clip data points and lines that are near the boundaries of a
 graph.

 Syntax:
       set clip <clip-type>
       set noclip <clip-type>
       show clip

 Three clip types are supported by `gnuplot`: `points`, `one`, and `two`.
 One, two, or all three clip types may be active for a single graph.

 The `points` clip type forces `gnuplot` to clip (actually, not plot at all)
 data points that fall within but too close to the boundaries.  This is done
 so that large symbols used for points will not extend outside the boundary
 lines.  Without clipping points near the boundaries, the plot may look bad.
 Adjusting the x and y ranges may give similar results.

 Setting the `one` clip type causes `gnuplot` to draw a line segment which has
 only one of its two endpoints within the graph.  Only the in-range portion of
 the line is drawn.  The alternative is to not draw any portion of the line
 segment.

 Some lines may have both endpoints out of range, but pass through the graph.
 Setting the `two` clip-type allows the visible portion of these lines to be
 drawn.

 In no case is a line drawn outside the graph.

 The defaults are `noclip points`, `clip one`, and `noclip two`.

 To check the state of all forms of clipping, use
       show clip

 For backward compatibility with older versions, the following forms are also
 permitted:
       set clip
       set noclip

 `set clip` is synonymous with `set clip points`; `set noclip` turns off all
 three types of clipping.
3 cntrparam
?commands set cntrparam
?commands show cntrparam
?set cntrparam
?show cntrparam
?cntrparam
 `set cntrparam` controls the generation of contours and their smoothness for
 a contour plot. `show contour` displays current settings of `cntrparam` as
 well as `contour`.

 Syntax:
       set cntrparam {  {linear | cubicspline | bspline}
                       { points <n>} { order <n> }
                       { levels   auto {<n>} | <n>
                                | discrete <z1> {,<z2>{,<z3>...}}
                                | incremental <start>, <incr> {,<end>}
                        }
                      }
       show contour

 This command has two functions.  First, it sets the values of z for which
 contour points are to be determined (by linear interpolation between data
 points or function isosamples.)  Second, it controls the way contours are
 drawn between the points determined to be of equal z.  <n> should be an
 integral constant expression and <z1>, <z2> ... any constant expressions.
 The parameters are:

 `linear`, `cubicspline`, `bspline`---Controls type of approximation or
 interpolation.  If `linear`, then straight line segments connect points of
 equal z magnitude.  If `cubicspline`, then piecewise-linear contours are
 interpolated between the same equal z points to form somewhat smoother
 contours, but which may undulate.  If `bspline`, a guaranteed-smoother curve
 is drawn, which only approximates the position of the points of equal-z.

 `points`---Eventually all drawings are done with piecewise-linear strokes.
 This number controls the number of line segments used to approximate the
 `bspline` or `cubicspline` curve.  Number of cubicspline or bspline
 segments (strokes) = `points` * number of linear segments.

 `order`---Order of the bspline approximation to be used.  The bigger this
 order is, the smoother the resulting contour.  (Of course, higher order
 bspline curves will move further away from the original piecewise linear
 data.)  This option is relevant for `bspline` mode only.  Allowed values are
 integers in the range from 2 (linear) to 10.

 `levels`--- Selection of contour levels,  controlled by `auto` (default),
 `discrete`, `incremental`, and <n>, number of contour levels, limited to
  MAX_DISCRETE_LEVELS as defined in plot.h (30 is standard.)

 For `auto`, <n> specifies a nominal number of levels; the actual number will
 be adjusted to give simple labels. If the surface is bounded by zmin and zmax,
 contours will be generated at integer multiples of dz between zmin and zmax,
 where dz is 1, 2, or 5 times some power of ten (like the step between two
 tic marks).

 For `levels discrete`, contours will be generated at z = <z1>, <z2> ... as
 specified; the number of discrete levels sets the number of contour levels.
 In `discrete` mode, any `set cntrparms levels <n>` are ignored.

 For `incremental`, contours are generated at values of z beginning at <start>
 and increasing by <increment>, until the number of contours is reached. <end>
 is used to determine the number of contour levels, which will be changed by
 any subsequent `set cntrparam levels <n>`.

 If the command `set cntrparam` is given without any arguments specified,  the
 defaults are used: linear, 5 points, order 4, 5 auto levels.

 Examples:
       set cntrparam bspline
       set cntrparam points 7
       set cntrparam order 10

 To select levels automatically, 5 if the level increment criteria are met:
       set cntrparam levels auto 5

 To specify discrete levels at .1, .37, and .9:
       set cntrparam levels discrete .1,1/exp(1),.9

 To specify levels from 0 to 4 with increment 1:
       set cntrparam levels incremental  0,1,4

 To set the number of levels to 10 (changing an incremental end or possibly
 the number of auto levels):
       set cntrparam levels 10

 To set the start and increment while retaining the number of levels:
       set cntrparam levels incremental 100,50

 See also `set contour` for control of where the contours are drawn, and `set
 clabel` for control of the format of the contour labels and linetypes.
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/contours.html">Contours Demo</a> and
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/discrete.html">contours with User Defined Levels.</a>
3 contour
?commands set contour
?commands set nocontour
?commands show contour
?set contour
?set nocontour
?show contour
?contour
?nocontour
 `set contour` enables contour drawing for surfaces. This option is available
 for `splot` only.

 Syntax:
       set contour {base | surface | both}
       set nocontour
       show contour

 The three options specify where to draw the contours: `base` draws the
 contours on the grid base where the x/ytics are placed, `surface` draws the
 contours on the surfaces themselves, and `both` draws the contours on both
 the base and the surface.  If no option is provided, the default is `base`.

 See also `set cntrparam` for the parameters that affect the drawing of
 contours, and `set clabel` for control of labelling of the contours.

 The surface can be switched off (see `set surface`), giving a contour-only
 graph.  Though it is possible to use `set size` to enlarge the plot to fill
 the screen, more control over the output format can be obtained by writing
 the contour information to a file, and rereading it as a 2-d datafile plot:

       set nosurface
       set contour
       set cntrparam ...
       set term table
       set out 'filename'
       splot ...
       set out
       # contour info now in filename
       set term <whatever>
       plot 'filename'

 In order to draw contours, the data should be organized as "grid data".  In
 such a file all the points for a single y-isoline are listed, then all the
 points for the next y-isoline, and so on.  A single blank line (a line
 containing no characters other than blank spaces and a carriage return and/or
 a line feed) separates one y-isoline from the next.  See also `splot datafile`.

 If contours are desired from non-grid data, `set dgrid3d` can be used to
 create an appropriate grid.  See `set dgrid3d` for more information.
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/contours.html">Contours Demo</a> and
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/discrete.html">contours with User Defined Levels.</a>
3 data style
?commands set data style
?commands show data style
?set data style
?show data style
?data style
 The `set data style` command changes the default plotting style for data
 plots.

 Syntax:
       set data style <style-choice>
       show data style

 See `set style` for the choices.  If no choice is given, the choices are
 listed.  `show data style` shows the current default data plotting style.
3 dgrid3d
?commands set dgrid3d
?commands set nodgrid3d
?commands show dgrid3d
?set dgrid3d
?set nodgrid3d
?show dgrid3d
?dgrid3d
?nodgrid3d
 The `set dgrid3d` command enables, and can set parameters for, non-grid
 to grid data mapping.

 Syntax:
       set dgrid3d {<row_size>} {,{<col_size>} {,<norm>}}
       set nodgrid3d
       show dgrid3d

 By default `dgrid3d` is disabled.  When enabled, 3-d data read from a file
 are always treated as a scattered data set.  A grid with dimensions derived
 from a bounding box of the scattered data and size as specified by the
 row/col_size parameters is created for plotting and contouring.  The grid
 is equally spaced in x (rows) and in y (columns); the z values are computed
 as weighted averages of the scattered points' z values.

 The third parameter, norm, controls the weighting:  Each data point is
 weighted inversely by its distance from the grid point raised to the norm
 power.  (Actually, the weights are given by the inverse of dx^norm + dy^norm,
 where dx and dy are the components of the separation of the grid point from
 each data point.  For some norms that are powers of two, specifically 4, 8,
 and 16, the computation is optimized by using the Euclidean distance in the
 weight calculation, (dx^2+dx^2)^norm/2.  However, any non-negative integer
 can be used.)

 The closer the data point is to a grid point, the more effect it has on
 that grid point and the larger the value of norm the less effect more
 distant data points have on that grid point.

 The `dgrid3d` option is a simple low pass filter that converts scattered
 data to a grid data set.  More sophisticated approaches to this problem
 exist and should be used to preprocess the data outside `gnuplot` if this
 simple solution is found inadequate.

 (The z values are found by weighting all data points, not by interpolating
 between nearby data points;  also edge effects may produce unexpected and/or
 undesired results.  In some cases, small norm values produce a grid point
 reflecting the average of distant data points rather than a local average,
 while large values of norm may produce "steps" with several grid points
 having the same value as the closest data point, rather than making a smooth
 transition between adjacent data points.  Some areas of a grid may be filled
 by extrapolation, to an arbitrary boundary condition.  The variables are
 not normalized; consequently the units used for x and y will affect the
 relative weights of points in the x and y directions.)

 Examples:
       set dgrid3d 10,10,1     # defaults
       set dgrid3d ,,4

 The first specifies that a grid of size 10 by 10 is to be constructed using
 a norm value of 1 in the weight computation.  The second only modifies the
 norm, changing it to 4.
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/scatter.html"> Dgrid3d Demo.</a>

3 dummy
?commands set dummy
?commands show dummy
?set dummy
?show dummy
?dummy
 The `set dummy` command changes the default dummy variable names.

 Syntax:
       set dummy {<dummy-var>} {,<dummy-var>}
       show dummy

 By default, `gnuplot` assumes that the independent, or "dummy", variable for
 the `plot` command is "t" if in parametric or polar mode, or "x" otherwise.
 Similarly the independent variables for the `splot` command are "u" and "v"
 in parametric mode (`splot` cannot be used in polar mode), or "x" and "y"
 otherwise.

 It may be more convenient to call a dummy variable by a more physically
 meaningful or conventional name.  For example, when plotting time functions:

       set dummy t
       plot sin(t), cos(t)

 At least one dummy variable must be set on the command; `set dummy` by itself
 will generate an error message.

 Examples:
       set dummy u,v
       set dummy ,s

 The second example sets the second variable to s.
3 encoding
?commands set encoding
?commands show encoding
?set encoding
?show encoding
?encoding
 The `set encoding` command selects a character encoding.  Valid values are
 `default`, which tells a terminal to use its default; `iso_8859_1` (known in
 the PostScript world as `ISO-Latin1`), which is used on many Unix workstations
 and with MS-Windows; `cp850`, for OS/2; and `cp437`, for MS-DOS.

 Syntax:
       set encoding {<value>}
       show encoding

 Note that encoding is not supported by all terminal drivers and that
 the device must be able to produce the desired non-standard characters.
3 format
?commands set format
?commands show format
?set format
?show format
?format
 The format of the tic-mark labels can be set with the `set format` command.

 Syntax:
       set format {<axes>} {"<format-string>"}
       set format {<axes>} {'<format-string>'}
       show format

 where <axes> is either `x`, `y`, `z`, `xy`, `x2`, `y2` or nothing (which is
 the same as `xy`).  The length of the string representing a tic mark (after
 formatting with 'printf') is restricted to 100 characters.  If the format
 string is omitted, the format will be returned to the default "%g".  For
 LaTeX users, the format "$%g$" is often desirable.  If the empty string "" is
 used, no label will be plotted with each tic, though the tic mark will still
 be plotted.  To eliminate all tic marks, use `set noxtics` or `set noytics`.

 Newline (\n) is accepted in the format string.  Use double-quotes rather than
 single-quotes to enable such interpretation.  See also `syntax`.

 The default format for both axes is "%g", but other formats such as "%.2f" or
 "%3.0em" are often desirable.  Anything accepted by 'printf' when given a
 double precision number, and accepted by the terminal, will work.  Some other
 options have been added.  If the format string looks like a floating point
 format, then `gnuplot` tries to construct a reasonable format.

 Characters not preceded by "%" are printed verbatim.  Thus you can include
 spaces and labels in your format string, such as "%g m", which will put " m"
 after each number.  If you want "%" itself, double it: "%g %%".

 See also `set xtics` for more information about tic labels.
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/electron.html"> See demo. </a>
4 format specifiers
?commands set format specifiers
?set format specifiers
?format specifiers
?format_specifiers
 The acceptable formats (if not in time/date mode) are:

@start table - first is interactive cleartext form
       Format       Explanation
       %f           floating point notation
       %e or %E     exponential notation; an "e" or "E" before the power
       %g or %G     the shorter of %e (or %E) and %f
       %x or %X     hex
       %o or %O     octal
       %t           mantissa to base 10
       %l           mantissa to base of current logscale
       %s           mantissa to base of current logscale; scientific power
       %T           power to base 10
       %L           power to base of current logscale
       %S           scientific power
       %c           character replacement for scientific power
       %P           multiple of pi
#\begin{tabular}{|cl|} \hline
#\multicolumn{2}{|c|}{Tic-mark label numerical format specifiers}\\
#\hline \hline
#Format & Explanation \\ \hline
#\verb@%f@ & floating point notation \\
#\verb@%e@ or \verb@%E@ & exponential notation; an "e" or "E" before the power \\
#\verb@%g@ or \verb@%G@ & the shorter of \verb@%e@ (or \verb@%E@) and \verb@%f@ \\
#\verb@%x@ or \verb@%X@ & hex \\
#\verb@%o@ or \verb@%O@ & octal \\
#\verb@%t@ & mantissa to base 10 \\
#\verb@%l@ & mantissa to base of current logscale \\
#\verb@%s@ & mantissa to base of current logscale; scientific power \\
#\verb@%T@ & power to base 10 \\
#\verb@%L@ & power to base of current logscale \\
#\verb@%S@ & scientific power \\
#\verb@%c@ & character replacement for scientific power \\
#\verb@%P@ & multiple of pi \\
%c l .
%Format@Explanation
%_
%%f@floating point notation
%%e or %E@exponential notation; an "e" or "E" before the power
%%g or %G@the shorter of %e (or %E) and %f
%%x or %X@hex
%%o or %O@octal
%%t@mantissa to base 10
%%l@mantissa to base of current logscale
%%s@mantissa to base of current logscale; scientific power
%%T@power to base 10
%%L@power to base of current logscale
%%S@scientific power
%%c@character replacement for scientific power
%%P@multiple of pi
%_
@end table

 A 'scientific' power is one such that the exponent is a multiple of three.
 Character replacement of scientific powers (`"%c"`) has been implemented
 for powers in the range -18 to +18.  For numbers outside of this range the
 format reverts to exponential.

 Other acceptable modifiers (which come after the "%" but before the format
 specifier) are "-", which left-justifies the number; "+", which forces all
 numbers to be explicitly signed; "#", which places a decimal point after
 floats that have only zeroes following the decimal point; a positive integer,
 which defines the field width; "0" (the digit, not the letter) immediately
 preceding the field width, which indicates that leading zeroes are to be used
 instead of leading blanks; and a decimal point followed by a non-negative
 integer, which defines the precision (the minimum number of digits of an
 integer, or the number of digits following the decimal point of a float).

 Some releases of 'printf' may not support all of these modifiers but may also
 support others; in case of doubt, check the appropriate documentation and
 then experiment.

 Examples:
       set format y "%t"; set ytics (5,10)          # "5.0" and "1.0"
       set format y "%s"; set ytics (500,1000)      # "500" and "1.0"
       set format y "+-12.3f"; set ytics(12345)     # "+12345.000  "
       set format y "%.2t*10^%+03T"; set ytic(12345)# "1.23*10^+04"
       set format y "%s*10^{%S}"; set ytic(12345)   # "12.345*10^{3}"
       set format y "%s %cg"; set ytic(12345)       # "12.345 kg"
       set format y "%.0P pi"; set ytic(6.283185)   # "2 pi"
       set format y "%.0P%%"; set ytic(50)          # "50%"

       set log y 2; set format y '%l'; set ytics (1,2,3)
       #displays "1.0", "1.0" and "1.5" (since 3 is 1.5 * 2^1)

 There are some problem cases that arise when numbers like 9.999 are printed
 with a format that requires both rounding and a power.

 If the data type for the axis is time/date, the format string must contain
 valid codes for the 'strftime' function (outside of `gnuplot`, type "man
 strftime").  See `set timefmt` for a list of the allowed input format codes.
4 time/date specifiers
?commands set format time/date_specifiers
?set format time/date_specifiers
?set time/date_specifiers
?time/date_specifiers
 In time/date mode, the acceptable formats are:

@start table - first is interactive cleartext form
       Format       Explanation
       %a           abbreviated name of day of the week
       %A           full name of day of the week
       %b or %h     abbreviated name of the month
       %B           full name of the month
       %d           day of the month, 1--31
       %D           shorthand for "%m/%d/%y"
       %H or %k     hour, 0--24
       %I or %l     hour, 0--12
       %j           day of the year, 1--366
       %m           month, 1--12
       %M           minute, 0--60
       %p           "am" or "pm"
       %r           shorthand for "%I:%M:%S %p"
       %R           shorthand for %H:%M"
       %S           second, 0--60
       %T           shorthand for "%H:%M:%S"
       %U           week of the year (week starts on Sunday)
       %w           day of the week, 0--6 (Sunday = 0)
       %W           week of the year (week starts on Monday)
       %y           year, 0-99
       %Y           year, 4-digit
#\begin{tabular}{|cl|} \hline
#\multicolumn{2}{|c|}{Tic-mark label Date/Time Format Specifiers}\\
#\hline \hline
#Format & Explanation \\ \hline
#\verb@%a@ & abbreviated name of day of the week \\
#\verb@%A@ & full name of day of the week \\
#\verb@%b@ or \verb@%h@ & abbreviated name of the month \\
#\verb@%B@ & full name of the month \\
#\verb@%d@ & day of the month, 1--31 \\
#\verb@%D@ & shorthand for \verb@"%m/%d/%y"@ \\
#\verb@%H@ or \verb@%k@ & hour, 0--24 \\
#\verb@%I@ or \verb@%l@ & hour, 0--12 \\
#\verb@%j@ & day of the year, 1--366 \\
#\verb@%m@ & month, 1--12 \\
#\verb@%M@ & minute, 0--60 \\
#\verb@%p@ & "am" or "pm" \\
#\verb@%r@ & shorthand for \verb@"%I:%M:%S %p"@ \\
#\verb@%R@ & shorthand for \verb@%H:%M"@ \\
#\verb@%S@ & second, 0--60 \\
#\verb@%T@ & shorthand for \verb@"%H:%M:%S"@ \\
#\verb@%U@ & week of the year (week starts on Sunday) \\
#\verb@%w@ & day of the week, 0--6 (Sunday = 0) \\
#\verb@%W@ & week of the year (week starts on Monday) \\
#\verb@%y@ & year, 0-99 \\
#\verb@%Y@ & year, 4-digit \\
%c l .
%Format@Explanation
%_
%%a@abbreviated name of day of the week
%%A@full name of day of the week
%%b or %h@abbreviated name of the month
%%B@full name of the month
%%d@day of the month, 1--31
%%D@shorthand for "%m/%d/%y"
%%H or %k@hour, 0--24
%%I or %l@hour, 0--12
%%j@day of the year, 1--366
%%m@month, 1--12
%%M@minute, 0--60
%%p@"am" or "pm"
%%r@shorthand for "%I:%M:%S %p"
%%R@shorthand for %H:%M"
%%S@second, 0--60
%%T@shorthand for "%H:%M:%S"
%%U@week of the year (week starts on Sunday)
%%w@day of the week, 0--6 (Sunday = 0)
%%W@week of the year (week starts on Monday)
%%y@year, 0-99
%%Y@year, 4-digit
%_
@end table

 Except for the non-numerical formats, these may be preceded by a "0" ("zero",
 not "oh") to pad the field length with leading zeroes, and a positive digit,
 to define the minimum field width (which will be overridden if the specified
 width is not large enough to contain the number).  There is a 24-character
 limit to the length of the printed text; longer strings will be truncated.

 Examples:

 Suppose the text is "76/12/25 23:11:11".  Then
       set format x                 # defaults to "12/25/76" \n "23:11"
       set format x "%A, %d %b %Y"  # "Saturday, 25 Dec 1976"
       set format x "%r %d"         # "11:11:11 pm 12/25/76"

 Suppose the text is "98/07/06 05:04:03".  Then
       set format x "%1y/%2m/%3d %01H:%02M:%03S"  # "98/ 7/  6 5:04:003"
3 function style
?commands set function style
?commands show function style
?set function style
?show function style
?function style
 The `set function style` command changes the default plotting style for
 function plots.

 Syntax:
       set function style <style-choice>
       show function style

 See `set style` for the choices.  If no choice is given, the choices are
 listed.  `show function style` shows the current default function plotting
 style.
3 functions
?commands show functions
?show functions
 The `show functions` command lists all user-defined functions and their
 definitions.

 Syntax:
       show functions

 For information about the definition and usage of functions in `gnuplot`,
 please see `expressions`.
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/spline.html"> Splines as User Defined Functions.</a>
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/airfoil.html">Use of functions and complex variables for airfoils </a>
3 grid
?commands set grid
?commands set nogrid
?commands show grid
?set grid
?set nogrid
?show grid
?grid
?nogrid
 The `set grid` command allows grid lines to be drawn on the plot.

 Syntax:
       set grid {{no}{m}xtics} {{no}{m}ytics} {{no}{m}ztics}
                {{no}{m}x2tics} {{no}{m}y2tics}
                {polar {<angle>}}
                { {linestyle <major_linestyle>}
                  | {linetype | lt <major_linetype>}
                    {linewidth | lw <major_linewidth>}
                  { , {linestyle | ls <minor_linestyle>}
                      | {linetype | lt <minor_linetype>}
                        {linewidth | lw <minor_linewidth>} } }
       set nogrid
       show grid

 The grid can be enabled and disabled for the major and/or minor tic
 marks on any axis, and the linetype and linewidth can be specified
 for major and minor grid lines, also via a predefined linestyle, as
 far as the active terminal driver supports this.

 Additionally, a polar grid can be selected for 2-d plots---circles are drawn
 to intersect the selected tics, and radial lines are drawn at definable
 intervals.  (The interval is given in degrees or radians ,depending on the
 `set angles` setting.)  Note that a polar grid is no longer automatically
 generated in polar mode.

 The pertinent tics must be enabled before `set grid` can draw them; `gnuplot`
 will quietly ignore instructions to draw grid lines at non-existent tics, but
 they will appear if the tics are subsequently enabled.

 If no linetype is specified for the minor gridlines, the same linetype as the
 major gridlines is used.  The default polar angle is 30 degrees.

 By default, grid lines are drawn with half the usual linewidth. The major and
 minor linewidth specifiers scale this default value; for example, `set grid
 lw .5` will draw grid lines with one quarter the usual linewidth.

 Z grid lines are drawn on the back of the plot.  This looks better if a
 partial box is drawn around the plot---see `set border`.
3 hidden3d
?commands set hidden3d
?commands set nohidden3d
?commands show hidden3d
?set hidden3d
?set nohidden3d
?show hidden3d
?hidden3d
?nohidden3d
 The `set hidden3d` command enables hidden line removal for surface plotting
 (see `splot`).  Some optional features of the underlying algorithm can also
 be controlled using this command.

 Syntax:
       set hidden3d {defaults} |
                    { {{offset <offset>} | {nooffset}}
                      {trianglepattern <bitpattern>}
                      {{undefined <level>} | {noundefined}}
                      {{no}altdiagonal}
                      {{no}bentover} }
       set nohidden3d
       show hidden3d

 In contrast to the usual display in gnuplot, hidden line removal actually
 treats the given function or data grids as real surfaces that can't be seen
 through, so parts behind the surface will be hidden by it.  For this to be
 possible, the surface needs to have 'grid structure' (see `splot datafile`
 about this), and it has to be drawn `with lines` or `with linespoints`.

 When `hidden3d` is set, both the hidden portion of the surface and possibly
 its contours drawn on the base (see `set contour`) as well as the grid will
 be hidden.  Each surface has its hidden parts removed with respect to itself
 and to other surfaces, if more than one surface is plotted.  Contours drawn
 on the surface (`set contour surface`) don't work.  Labels and arrows are
 always visible and are unaffected.  The key is also never hidden by the
 surface.

 Functions are evaluated at isoline intersections.  The algorithm interpolates
 linearly between function points or data points when determining the visible
 line segments.  This means that the appearance of a function may be different
 when plotted with `hidden3d` than when plotted with `nohidden3d` because in
 the latter case functions are evaluated at each sample.  Please see `set
 samples` and `set isosamples` for discussion of the difference.

 The algorithm used to remove the hidden parts of the surfaces has some
 additional features controllable by this command.  Specifying `defaults` will
 set them all to their default settings, as detailed below.  If `defaults` is
 not given, only explicitly specified options will be influenced: all others
 will keep their previous values, so you can turn on/off hidden line removal
 via `set {no}hidden3d`, without modifying the set of options you chose.

 The first option, `offset`, influences the linestyle used for lines on the
 'back' side.  Normally, they are drawn in a linestyle one index number higher
 than the one used for the front, to make the two sides of the surface
 distinguishable.  You can specify a different line style offset to add
 instead of the default 1, by `offset <offset>`.  Option `nooffset` stands for
 `offset 0`, making the two sides of the surface use the same linestyle.

 Next comes the option `trianglepattern <bitpattern>`.  <bitpattern> must be
 a number between 0 and 7, interpreted as a bit pattern.  Each bit determines
 the visibility of one edge of the triangles each surface is split up into.
 Bit 0 is for the 'horizontal' edges of the grid, Bit 1 for the 'vertical'
 ones, and Bit 2 for the diagonals that split each cell of the original grid
 into two triangles.  The default pattern is 3, making all horizontal and
 vertical lines visible, but not the diagonals.  You may want to choose 7 to
 see those diagonals as well.

 The `undefined <level>` option lets you decide what the algorithm is to do
 with data points that are undefined (missing data, or undefined function
 values), or exceed the given x-, y- or z-ranges.  Such points can either be
 plotted nevertheless, or taken out of the input data set.  All surface
 elements touching a point that is taken out will be taken out as well, thus
 creating a hole in the surface.  If <level> = 3, equivalent to option
 `noundefined`, no points will be thrown away at all.  This may produce all
 kinds of problems elsewhere, so you should avoid this.  <level> = 2 will
 throw away undefined points, but keep the out-of-range ones.  <level> = 1,
 the default, will get rid of out-of-range points as well.

 By specifying `noaltdiagonal`, you can override the default handling of a
 special case can occur if `undefined` is active (i.e. <level> is not 3).
 Each cell of the grid-structured input surface will be divided in two
 triangles along one of its diagonals.  Normally, all these diagonals have
 the same orientation relative to the grid.  If exactly one of the four cell
 corners is excluded by the `undefined` handler, and this is on the usual
 diagonal, both triangles will be excluded.  However if the default setting
 of `altdiagonal` is active, the other diagonal will be chosen for this cell
 instead, minimizing the size of the hole in the surface.

 The `bentover` option controls what happens to another special case, this
 time in conjunction with the `trianglepattern`.  For rather crumply surfaces,
 it can happen that the two triangles a surface cell is divided into are seen
 from opposite sides (i.e. the original quadrangle is 'bent over'), as
 illustrated in the following ASCII art:

                                                               C----B
     original quadrangle:  A--B      displayed quadrangle:     |\   |
       ("set view 0,0")    | /|    ("set view 75,75" perhaps)  | \  |
                           |/ |                                |  \ |
                           C--D                                |   \|
                                                               A    D

 If the diagonal edges of the surface cells aren't generally made visible by
 bit 2 of the <bitpattern> there, the edge CB above wouldn't be drawn at all,
 normally, making the resulting display hard to understand.  Therefore, the
 default option of `bentover` will turn it visible in this case.  If you don't
 want that, you may choose `nobentover` instead.
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/hidden.html"> Hidden Line Removal Demo</a> and
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/singulr.html"> Complex Hidden Line Demo. </a>
3 isosamples
?commands set isosamples
?commands show isosamples
?set isosamples
?show isosamples
?isosamples
 The isoline density (grid) for plotting functions as surfaces may be changed
 by the `set isosamples` command.

 Syntax:
       set isosamples <iso_1> {,<iso_2>}
       show isosamples

 Each function surface plot will have <iso_1> iso-u lines and <iso_2> iso-v
 lines.  If you only specify <iso_1>, <iso_2> will be set to the same value
 as <iso_1>.  By default, sampling is set to 10 isolines per u or v axis.
 A higher sampling rate will produce more accurate plots, but will take longer.
 These parameters have no effect on data file plotting.

 An isoline is a curve parameterized by one of the surface parameters while
 the other surface parameter is fixed.  Isolines provide a simple means to
 display a surface.  By fixing the u parameter of surface s(u,v), the iso-u
 lines of the form c(v) = s(u0,v) are produced, and by fixing the v parameter,
 the iso-v lines of the form c(u) = s(u,v0) are produced.

 When a function surface plot is being done without the removal of hidden
 lines, `set samples`  controls the number of points sampled along each
 isoline;  see `set samples` and `set hidden3d`.  The contour algorithm
 assumes that a function sample occurs at each isoline intersection, so
 change in `samples` as well as `isosamples` may be desired when changing
 the resolution of a function surface/contour.
3 key
?commands set key
?commands set nokey
?commands show key
?set key
?set nokey
?show key
?key
?nokey
?legend
 The `set key` enables a key (or legend) describing plots on a plot.

 The contents of the key, i.e., the names given to each plotted data set and
 function and samples of the lines and/or symbols used to represent them, are
 determined by the `title` and `with` options of the {`s`}`plot` command.
 Please see `plot title` and `plot with` for more information.

 Syntax:
       set key {  left | right | top | bottom | outside | below
                | <position>}
               {Left | Right} {{no}reverse}
               {samplen <sample_length>} {spacing <vertical_spacing>}
               {width <width_increment>}
               {title "<text>"}
               {{no}box { {linestyle | ls <line_style>}
                          | {linetype | lt <line_type>}
                            {linewidth | lw <line_width>}}}
       set nokey
       show key

 By default the key is placed in the upper right corner of the graph.  The
 keywords `left`, `right`, `top`, `bottom`, `outside` and `below` may be used
 to place the key in the other corners inside the graph or to the right
 (outside) or below the graph.  They may be given alone or combined.

 Justification of the labels within the key is controlled by `Left` or `Right`
 (default is `Right`).  The text and sample can be reversed (`reverse`) and a
 box can be drawn around the key (`box {...}`) in a specified `linetype`
 and `linewidth`, or a user-defined `linestyle`. Note that not all
 terminal drivers support linewidth selection, though.

 The length of the sample line can be controlled by `samplen`.  The sample
 length is computed as the sum of the tic length and <sample_length> times the
 character width.  `samplen` also affects the positions of point samples in
 the key since these are drawn at the midpoint of the sample line, even if it
 is not drawn.  <sample_length> must be an integer.

 The vertical spacing between lines is controlled by `spacing`.  The spacing
 is set equal to the product of the pointsize, the vertical tic size, and
 <vertical_spacing>.  The program will guarantee that the vertical spacing is
 no smaller than the character height.

 The <width_increment> is a number of character widths to be added to or
 subtracted from the length of the string.  This is useful only when you are
 putting a box around the key and you are using control characters in the text.
 `gnuplot` simply counts the number of characters in the string when computing
 the box width; this allows you to correct it.

 A title can be put on the key (`title "<text>"`)---see also `syntax` for the
 distinction between text in single- or double-quotes.  The key title uses the
 same justification as do the plot titles.

 The defaults for `set key` are `right`, `top`, `Right`, `noreverse`, `samplen
 4`, `spacing 1.25`, `title ""`, and `nobox`.  The default <linetype> is the
 same as that used for the plot borders.  Entering `set key` with no options
 returns the key to its default configuration.

 The <position> can be a simple x,y,z as in previous versions, but these can
 be preceded by one of four keywords (`first`, `second`, `graph`, `screen`)
 which selects the coordinate system in which the position is specified.  See
 `coordinates` for more details.

 The key is drawn as a sequence of lines, with one plot described on each
 line.  On the right-hand side (or the left-hand side, if `reverse` is
 selected) of each line is a representation that attempts to mimic the way the
 curve is plotted.  On the other side of each line is the text description
 (the line title), obtained from the `plot` command.  The lines are vertically
 arranged so that an imaginary straight line divides the left- and right-hand
 sides of the key.  It is the coordinates of the top of this line that are
 specified with the `set key` command.  In a `plot`, only the x and y
 coordinates are used to specify the line position.  For a `splot`, x, y and
 z are all used as a 3-d location mapped using the same mapping as the graph
 itself to form the required 2-d screen position of the imaginary line.

 Some or all of the key may be outside of the graph boundary, although this
 may interfere with other labels and may cause an error on some devices.  If
 you use the keywords `outside` or `below`, `gnuplot` makes space for the keys
 and the graph becomes smaller.  Putting keys outside to the right, they
 occupy as few columns as possible, and putting them below, as many columns as
 possible (depending of the length of the labels), thus stealing as little
 space from the graph as possible.

 When using the TeX or PostScript drivers, or similar drivers where formatting
 information is embedded in the string, `gnuplot` is unable to calculate
 correctly the width of the string for key positioning.  If the key is to be
 positioned at the left, it may be convenient to use the combination  `set key
 left Left reverse`.  The box and gap in the grid will be the width of the
 literal string.

 If `splot` is being used to draw contours, the contour labels will be listed
 in the key.  If the alignment of these labels is poor or a different number
 of decimal places is desired, the label format can be specified.  See `set
 clabel` for details.

 Examples:

 This places the key at the default location:
       set key

 This disables the key:
       set nokey

 This places a key at coordinates 2,3.5,2 in the default (first) coordinate
 system:
       set key 2,3.5,2

 This places the key below the graph:
       set key below

 This places the key in the bottom left corner, left-justifies the text,
 gives it a title, and draws a box around it in linetype 3:
       set key left bottom Left title 'Legend' box 3
3 label
?commands set label
?commands set nolabel
?commands show label
?set label
?set nolabel
?show label
?label
?nolabel
 Arbitrary labels can be placed on the plot using the `set label` command.

 Syntax:
       set label {<tag>} {"<label_text>"} {at <position>}
                 {<justification>} {{no}rotate} {font "<name><,size>"}
       set nolabel {<tag>}
       show label

 The <position> is specified by either x,y or x,y,z, and may be preceded by
 `first`, `second`, `graph`, or `screen` to select the coordinate system.
 See `coordinates` for details.

 The tag is an integer that is used to identify the label. If no <tag> is
 given, the lowest unused tag value is assigned automatically.  The tag can be
 used to delete or modify a specific label.  To change any attribute of an
 existing label, use the `set label` command with the appropriate tag, and
 specify the parts of the label to be changed.

 By default, the text is placed flush left against the point x,y,z.  To adjust
 the way the label is positioned with respect to the point x,y,z, add the
 parameter <justification>, which may be `left`, `right` or `center`,
 indicating that the point is to be at the left, right or center of the text.
 Labels outside the plotted boundaries are permitted but may interfere with
 axis labels or other text.

 If `rotate` is given, the label is written vertically (if the terminal can do
 so, of course).

 If one (or more) axis is timeseries, the appropriate coordinate should be
 given as a quoted time string according to the `timefmt` format string.  See
 `set xdata` and `set timefmt`.

 The EEPIC, Imagen, LaTeX, and TPIC drivers allow \\ in a string to specify
 a newline.

 Examples:

 To set a label at (1,2) to "y=x", use:
       set label "y=x" at 1,2

 To set a Sigma of size 24, from the Symbol font set, at the center of
 the graph, use:
       set label "S" at graph 0.5,0.5 center font "Symbol,24"

 To set a label "y=x^2" with the right of the text at (2,3,4), and tag the
 label as number 3, use:
       set label 3 "y=x^2" at 2,3,4 right

 To change the preceding label to center justification, use:
       set label 3 center

 To delete label number 2, use:
       set nolabel 2

 To delete all labels, use:
       set nolabel

 To show all labels (in tag order), use:
       show label

 To set a label on a graph with a timeseries on the x axis, use, for example:
       set timefmt "%d/%m/%y,%H:%M"
       set label "Harvest" at "25/8/93",1
3 linestyle
?commands set linestyle
?commands set nolinestyle
?commands show linestyle
?set linestyle
?set nolinestyle
?show linestyle
?linestyle
 Each terminal has a default set of line and point types, which can be seen
 by using the command `test`.  `set linestyle` defines a set of line types
 and widths and point types and sizes so that you can refer to them later by
 an index instead of repeating all the information at each invocation.

 Syntax:
       set linestyle <index> {linetype | lt <line_type>}
                             {linewidth | lw <line_width>}
                             {pointtype | pt <point_type>}
                             {pointsize | ps <point_size>}
       set nolinestyle
       show linestyle

 The line and point types are taken from the default types for the terminal
 currently in use.  The line width and point size are multipliers for the
 default width and size (but note that <point_size> here is unaffected by
 the multiplier given on 'set pointsize').

 The defaults for the line and point types is the index.  The defaults for
 the width and size are both unity.

 Linestyles created by this mechanism do not replace the default styles;
 both may be used.

 Not all terminals support the `linewidth` and `pointsize` features; if
 not supported, the option will be ignored.

 Note that this feature is not completely implemented; linestyles defined by
 this mechanism may be used with 'plot', 'splot', 'replot', and 'set arrow',
 but not by other commands that allow the default index to be used, such as
 'set grid'.

 Example:
 Suppose that the default lines for indices 1, 2, and 3 are red, green, and
 blue, respectively, and the default point shapes for the same indices are a
 square, a cross, and a triangle, respectively.  Then

       set linestyle 1 lt 2 lw 2 pt 3 ps 0.5

 defines a new linestyle that is green and twice the default width and a new
 pointstyle that is a half-sized triangle.  The commands

       set function style lines
       plot f(x) lt 3, g(x) ls 1

 will create a plot of f(x) using the default blue line and a plot of g(x)
 using the user-defined wide green line.  Similarly the commands

       set function style linespoints
       plot p(x) lt 1 pt 3, q(x) ls 1

 will create a plot of f(x) using the default triangles connected by a red
 line and q(x) using small triangles connected by a green line.
3 lmargin
?commands set lmargin
?set lmargin
?lmargin
 The command `set lmargin` sets the size of the left margin.  Please see
 `set margin` for details.
3 locale
?commands set locale
?commands show logscale
?set locale
?show logscale
?locale
 The `locale` setting determines the language with which `{x,y,z}{d,m}tics`
 will write the days and months.

 Syntax:
       set locale {"<locale>"}

 <locale> may be any language designation acceptable to your installation.
 See your system documentation for the available options.  The default value
 is determined from the LANG environment variable.
3 logscale
?commands set logscale
?commands set nologscale
?commands show logscale
?set logscale
?set nologscale
?show logscale
?logscale
?nologscale
 Log scaling may be set on the x, y, z, x2 and/or y2 axes.

 Syntax:
       set logscale <axes> <base>
       set nologscale <axes>
       show logscale

 where <axes> may be any combinations of `x`, `y`, and `z`, in any order, or
 `x2` or `y2` and where <base> is the base of the log scaling.  If <base> is
 not given, then 10 is assumed.  If <axes> is not given, then all axes are
 assumed.  `set nologscale` turns off log scaling for the specified axes.

 Examples:

 To enable log scaling in both x and z axes:
       set logscale xz

 To enable scaling log base 2 of the y axis:
       set logscale y 2

 To disable z axis log scaling:
       set nologscale z
3 mapping
?commands set mapping
?commands show mapping
?set mapping
?show mapping
?mapping
 If data are provided to `splot` in spherical or cylindrical coordinates,
 the `set mapping` command should be used to instruct `gnuplot` how to
 interpret them.

 Syntax:
       set mapping {cartesian | spherical | cylindrical}

 A cartesian coordinate system is used by default.

 For a spherical coordinate system, the data occupy two or three columns (or
 `using` entries).  The first two are interpreted as the polar and azimuthal
 angles theta and phi (in the units specified by `set angles`).  The radius r
 is taken from the third column if there is one, or is set to unity if there
 is no third column.  The mapping is:

       x = r * cos(theta) * cos(phi)
       y = r * sin(theta) * cos(phi)
       z = r * sin(phi)

 Note that this is a "geographic" spherical system, rather than a "polar" one.

 For a cylindrical coordinate system, the data again occupy two or three
 columns.  The first two are interpreted as theta (in the units specified by
 `set angles`) and z.  The radius is either taken from the third column or set
 to unity, as in the spherical case.  The mapping is:

       x = r * cos(theta)
       y = r * sin(theta)
       z = z

 The effects of `mapping` can be duplicated with the `using` filter on the
 `splot` command, but `mapping` may be more convenient if many data files are
 to be processed.  However even if `mapping` is used, `using` may still be
 necessary if the data in the file are not in the required order.

 `mapping` has no effect on `plot`.
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/world.html">Mapping Demos.</a>
3 margin
?commands set margin
?commands show margin
?set margin
?show margin
?margin
 The computed margins can be overridden by the `set margin` commands.  `show
 margin` shows the current settings.

 Syntax:
       set bmargin {<margin>}
       set lmargin {<margin>}
       set rmargin {<margin>}
       set tmargin {<margin>}
       show margin

 The units of <margin> are character heights or widths, as appropriate.  A
 positive value defines the absolute size of the margin.  A negative value
 (or none) causes `gnuplot` to revert to the computed value.

 Normally the margins of a plot are automatically calculated based on tics,
 tic labels, axis labels, the plot title, the timestamp and the size of the
 key if it is outside the borders.  If, however, tics are attached to the
 axes (`set xtics axis`, for example), neither the tics themselves nor their
 labels will be included in either the margin calculation or the calculation
 of the positions of other text to be written in the margin.  This can lead
 to tic labels overwriting other text if the axis is very close to the border.
3 missing
?commands set missing
?set missing
?missing
 The `set missing` command allows you to tell `gnuplot` what character is
 used in a data file to denote missing data.

 Syntax:
       set missing {"<character>"}
       show missing

 Example:
       set missing "?"

 would mean that, when plotting a file containing

          1 1
          2 ?
          3 2

 the middle line would be ignored.

 There is no default character for `missing`.
3 multiplot
?commands set multiplot
?commands set nomultiplot
?set multiplot
?set nomultiplot
?multiplot
?nomultiplot
 The command `set multiplot` places `gnuplot` in the multiplot mode, in which
 several plots are placed on the same page, window, or screen.

 Syntax:
       set multiplot
       set nomultiplot

 For some terminals, no plot is displayed until the command `set nomultiplot`
 is given, which causes the entire page to be drawn and then returns `gnuplot`
 to its normal single-plot mode.  For other terminals, each separate `plot`
 command produces a plot, but the screen may not be cleared between plots.

 Any labels or arrows that have been defined will be drawn for each plot
 according to the current size and origin (unless their coordinates are
 defined in the `screen` system).  Just about everything else that can be
 `set` is applied to each plot, too.  If you want something to appear only
 once on the page, for instance a single time stamp, you'll need to put a `set
 time`/`set notime` pair around one of the `plot`, `splot` or `replot`
 commands within the `set multiplot`/`set nomultiplot` block.

 The commands `set origin` and `set size` must be used to correctly position
 each plot; see `set origin` and `set size` for details of their usage.

 Example:
       set size 0.7,0.7
       set origin 0.1,0.1
       set multiplot
       set size 0.4,0.4
       set origin 0.1,0.1
       plot sin(x)
       set size 0.2,0.2
       set origin 0.5,0.5
       plot cos(x)
       set nomultiplot

 displays a plot of cos(x) stacked above a plot of sin(x).  Note the initial
 `set size` and `set origin`.  While these are not always required, their
 inclusion is recommended.  Some terminal drivers require that bounding box
 information be available before any plots can be made, and the form given
 above guarantees that the bounding box will include the entire plot array
 rather than just the bounding box of the first plot.

 `set size` and `set origin` refer to the entire plotting area used for each
 plot.  If you want to have the axes themselves line up, you can guarantee
 that the margins are the same size with the `set margin` commands.  See
 `set margin` for their use.  Note that the margin settings are absolute,
 in character units, so the appearance of the graph in the remaining space
 will depend on the screen size of the display device, e.g., perhaps quite
 different on a video display and a printer.
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/multiplt.html"> See demo. </a>
3 mx2tics
?commands set mx2tics
?commands set nomx2tics
?commands show mx2tics
?set mx2tics
?set nomx2tics
?show mx2tics
?mx2tics
?nomx2tics
 Minor tic marks along the x2 (top) axis are controlled by `set mx2tics`.
 Please see `set mxtics`.
3 mxtics
?commands set mxtics
?commands set nomxtics
?commands show mxtics
?set mxtics
?set nomxtics
?show mxtics
?mxtics
?nomxtics
 Minor tic marks along the x axis are controlled by `set mxtics`.  They can be
 turned off with `set nomxtics`.  Similar commands control minor tics along
 the other axes.

 Syntax:
       set mxtics {<freq> | default}
       set nomxtics
       show mxtics

 The same syntax applies to `mytics`, `mztics`, `mx2tics` and `my2tics`.

 <freq> is the number of sub-intervals (NOT the number of minor tics) between
 major tics (ten is the default for a linear axis, so there are nine minor
 tics between major tics). Selecting `default` will return the number of minor
 ticks to its default value.

 If the axis is logarithmic, the number of sub-intervals will be set to a
 reasonable number by default (based upon the length of a decade).  This will
 be overridden if <freq> is given.  However the usual minor tics (2, 3, ...,
 8, 9 between 1 and 10, for example) are obtained by setting <freq> to 10,
 even though there are but nine sub-intervals.

 Minor tics can be used only with uniformly spaced major tics.  Since major
 tics can be placed arbitrarily by `set {x|x2|y|y2|z}tics`, minor tics cannot
 be used if major tics are explicitly `set`.

 By default, minor tics are off for linear axes and on for logarithmic axes.
 They inherit the settings for `axis|border` and `{no}mirror` specified for
 the major tics.  Please see `set xtics` for information about these.
3 my2tics
?commands set my2tics
?commands set nomy2tics
?commands show my2tics
?set my2tics
?set nomy2tics
?show my2tics
?my2tics
?nomy2tics
 Minor tic marks along the y2 (right-hand) axis are controlled by `set
 my2tics`.  Please see `set mxtics`.
3 mytics
?commands set mytics
?commands set nomytics
?commands show mytics
?set mytics
?set nomytics
?show mytics
?mytics
?nomytics
 Minor tic marks along the y axis are controlled by `set mytics`.  Please
 see `set mxtics`.
3 mztics
?commands set mztics
?commands set nomztics
?commands show mztics
?set mztics
?set nomztics
?show mztics
?mztics
?nomztics
 Minor tic marks along the z axis are controlled by `set mztics`.  Please
 see `set mxtics`.
3 offsets
?commands set offsets
?commands set nooffsets
?commands show offsets
?set offsets
?set nooffsets
?show offsets
?offsets
?nooffsets
 Offsets provide a mechanism to put a boundary around the data inside of an
 autoscaled graph.

 Syntax:
       set offsets <left>, <right>, <top>, <bottom>
       set nooffsets
       show offsets

 Each offset may be a constant or an expression.  Each defaults to 0.  Left
 and right offsets are given in units of the x axis, top and bottom offsets in
 units of the y axis.  A positive offset expands the graph in the specified
 direction, e.g., a positive bottom offset makes ymin more negative.  Negative
 offsets, while permitted, can have unexpected interactions with autoscaling
 and clipping.

 Offsets are ignored in `splot`s.

 Example:
       set offsets 0, 0, 2, 2
       plot sin(x)

 This graph of sin(x) will have a y range [-3:3] because the function
 will be autoscaled to [-1:1] and the vertical offsets are each two.
3 origin
?commands set origin
?commands show origin
?set origin
?show origin
?origin
 The `set origin` command is used to specify the origin of a plotting surface
 (i.e., the graph and its margins) on the screen.  The coordinates are given
 in the `screen` coordinate system (see `coordinates` for information about
 this system).

 Syntax:
       set origin <x-origin>,<y-origin>
3 output
?commands set output
?commands show output
?set output
?show output
?output
 By default, screens are displayed to the standard output. The `set output`
 command redirects the display to the specified file or device.

 Syntax:
       set output {"<filename>"}
       show output

 The filename must be enclosed in quotes.  If the filename is omitted, any
 output file opened by a previous invocation of `set output` will be closed
 and new output will be sent to STDOUT.  (If you give the command `set output
 "STDOUT"`, your output may be sent to a file named "STDOUT"!  ["May be", not
 "will be", because some terminals, like `x11`, ignore `set output`.])

 MSDOS users should note that the \ character has special significance in
 double-quoted strings, so single-quotes should be used for filenames in
 different directories.

 When both `set terminal` and `set output` are used together, it is safest to
 give `set terminal` first, because some terminals set a flag which is needed
 in some operating systems.  This would be the case, for example, if the
 operating system needs to know whether or not a file is to be formatted in
 order to open it properly.

 On machines with popen functions (Unix), output can be piped through a shell
 command if the first non-whitespace character of the filename is '|'.
 For instance,

       set output "|lpr -Plaser filename"
       set output "|lp -dlaser filename"

 On MSDOS machines, `set output "PRN"` will direct the output to the default
 printer.  On VMS, output can be sent directly to any spooled device.  It is
 also possible to send the output to DECnet transparent tasks, which allows
 some flexibility.
3 parametric
?commands set parametric
?commands set noparametric
?commands show parametric
?set parametric
?set noparametric
?show parametric
?parametric
?noparametric
 The `set parametric` command changes the meaning of `plot` (`splot`) from
 normal functions to parametric functions.  The command `set noparametric`
 restores the plotting style to normal, single-valued expression plotting.

 Syntax:
       set parametric
       set noparametric
       show parametric

 For 2-d plotting, a parametric function is determined by a pair of parametric
 functions operating on a parameter.  An example of a 2-d parametric function
 would be `plot sin(t),cos(t)`, which draws a circle (if the aspect ratio is
 set correctly---see `set size`).  `gnuplot` will display an error message if
 both functions are not provided for a parametric `plot`.

 For 3-d plotting, the surface is described as x=f(u,v), y=g(u,v), z=h(u,v).
 Therefore a triplet of functions is required.  An example of a 3-d parametric
 function would be `cos(u)*cos(v),cos(u)*sin(v),sin(u)`, which draws a sphere.
 `gnuplot` will display an error message if all three functions are not
 provided for a parametric `splot`.

 The total set of possible plots is a superset of the simple f(x) style plots,
 since the two functions can describe the x and y values to be computed
 separately.  In fact, plots of the type t,f(t) are equivalent to those
 produced with f(x) because the x values are computed using the identity
 function.  Similarly, 3-d plots of the type u,v,f(u,v) are equivalent to
 f(x,y).

 Note that the order the parametric functions are specified is xfunction,
 yfunction (and zfunction) and that each operates over the common parametric
 domain.

 Also, the `set parametric` function implies a new range of values.  Whereas
 the normal f(x) and f(x,y) style plotting assume an xrange and yrange (and
 zrange), the parametric mode additionally specifies a trange, urange, and
 vrange.  These ranges may be set directly with `set trange`, `set urange`,
 and `set vrange`, or by specifying the range on the `plot` or `splot`
 commands.  Currently the default range for these parametric variables is
 [-5:5].  Setting the ranges to something more meaningful is expected.
3 pointsize
?commands set pointsize
?commands show pointsize
?set pointsize
?show pointsize
?pointsize
 The `set pointsize` command scales the size of the points used in plots.

 Syntax:
       set pointsize <multiplier>
       show pointsize

 The default is a multiplier of 1.0.  Larger pointsizes may be useful to
 make points more visible in bitmapped graphics.

 The pointsize of a single plot may be changed on the `plot` command.  See
 `plot with` for details.

 Please note that the pointsize setting is not supported by all terminal
 types.
3 polar
?commands set polar
?commands set nopolar
?commands show polar
?set polar
?set nopolar
?show polar
?polar
?nopolar
 The `set polar` command changes the meaning of the plot from rectangular
 coordinates to polar coordinates.

 Syntax:
       set polar
       set nopolar
       show polar

 There have been changes made to polar mode in version 3.7, so that scripts
 for `gnuplot` versions 3.5 and earlier will require modification.  The main
 change is that the dummy variable t is used for the angle so that the x and
 y ranges can be controlled independently.  Other changes are:
 1) tics are no longer put along the zero axes automatically
 ---use `set xtics axis nomirror`; `set ytics axis nomirror`;
 2) the grid, if selected, is not automatically polar
 ---use `set grid polar`;
 3) the grid is not labelled with angles
 ---use `set label` as necessary.

 In polar coordinates, the dummy variable (t) is an angle.  The default range
 of t is [0:2*pi], or, if degree units have been selected, to [0:360] (see
 `set angles`).

 The command `set nopolar` changes the meaning of the plot back to the default
 rectangular coordinate system.

 The `set polar` command is not supported for `splot`s.  See the `set mapping`
 command for similar functionality for `splot`s.

 While in polar coordinates the meaning of an expression in t is really
 r = f(t), where t is an angle of rotation.  The trange controls the domain
 (the angle) of the function, and the x and y ranges control the range of the
 graph in the x and y directions.  Each of these ranges, as well as the
 rrange, may be autoscaled or set explicitly.  See `set xrange` for details
 of all the `set range` commands.

 Example:
       set polar
       plot t*sin(t)
       plot [-2*pi:2*pi] [-3:3] [-3:3] t*sin(t)

 The first `plot` uses the default polar angular domain of 0 to 2*pi.  The
 radius and the size of the graph are scaled automatically.  The second `plot`
 expands the domain, and restricts the size of the graph to [-3:3] in both
 directions.

 You may want to `set size square` to have `gnuplot` try to make the aspect
 ratio equal to unity, so that circles look circular.
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/polar.html">Polar demos </a>
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/poldat.html">Polar Data Plot. </a>
3 rmargin
?commands set rmargin
?set rmargin
?rmargin
 The command `set rmargin` sets the size of the right margin.  Please see
 `set margin` for details.
3 rrange
?commands set rrange
?commands show rrange
?set rrange
?show rrange
?rrange
 The `set rrange` command sets the range of the radial coordinate for a
 graph in polar mode.  Please see `set xrange` for details.
3 samples
?commands set samples
?commands show samples
?set samples
?show samples
?samples
 The sampling rate of functions, or for interpolating data, may be changed
 by the `set samples` command.

 Syntax:
       set samples <samples_1> {,<samples_2>}
       show samples

 By default, sampling is set to 100 points.  A higher sampling rate will
 produce more accurate plots, but will take longer.  This parameter has no
 effect on data file plotting unless one of the interpolation/approximation
 options is used.  See `plot smooth` re 2-d data and `set cntrparam` and
 `set dgrid3d` re 3-d data.

 When a 2-d graph is being done, only the value of <samples_1> is relevant.

 When a surface plot is being done without the removal of hidden lines, the
 value of samples specifies the number of samples that are to be evaluated for
 the isolines.  Each iso-v line will have <sample_1> samples and each iso-u
 line will have <sample_2> samples.  If you only specify <samples_1>,
 <samples_2> will be set to the same value as <samples_1>.  See also `set
 isosamples`.
3 size
?commands set size
?commands show size
?set size
?show size
?size
 The `set size` command scales the displayed size of the plot.

 Syntax:
       set size {{no}square | ratio <r> | noratio} {<xscale>,<yscale>}
       show size

 The <xscale> and <yscale> values are the scaling factors for the size of the
 plot, which includes the graph and the margins.

 `ratio` causes `gnuplot` to try to create a graph with an aspect ratio of <r>
 (the ratio of the y-axis length to the x-axis length) within the portion of
 the plot specified by <xscale> and <yscale>.

 The meaning of a negative value for <r> is different.  If <r>=-1, gnuplot
 tries to set the scales so that the unit has the same length on both the x
 and y axes (suitable for geographical data, for instance).  If <r>=-2, the
 unit on y has twice the length of the unit on x, and so on.

 The success of `gnuplot` in producing the requested aspect ratio depends on
 the terminal selected.  The graph area will be the largest rectangle of
 aspect ratio <r> that will fit into the specified portion of the output
 (leaving adequate margins, of course).

 `square` is a synonym for `ratio 1`.

 Both `noratio` and `nosquare` return the graph to the default aspect ratio
 of the terminal, but do not return <xscale> or <yscale> to their default
 values (1.0).

 `ratio` and `square` have no effect on 3-d plots.

 `set size` is relative to the default size, which differs from terminal to
 terminal.  Since `gnuplot` fills as much of the available plotting area as
 possible by default, it is safer to use `set size` to decrease the size of
 a plot than to increase it.  See `set terminal` for the default sizes.

 On some terminals, changing the size of the plot will result in text being
 misplaced.

 Examples:

 To set the size to normal size use:
       set size 1,1

 To make the graph half size and square use:
       set size square 0.5,0.5

 To make the graph twice as high as wide use:
       set size ratio 2

^<a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/airfoil.html"> See demo. </a>
3 style
?commands set function style
?commands show function style
?commands set data style
?commands show data style
?set function style
?show function style
?set data style
?show data style
?set style
?show style
 Default styles are chosen with the `set function style` and `set data style`
 commands.  See `plot with` for information about how to override the default
 plotting style for individual functions and data sets.

 Syntax:
       set function style <style>
       set data style <style>
       show function style
       show data style

 The types used for all line and point styles (i.e., solid, dash-dot, color,
 etc. for lines; circles, squares, crosses, etc. for points) will be either
 those specified on the `plot` or `splot` command or will be chosen
 sequentially from the types available to the terminal in use.  Use the
 command `test` to see what is available.

 None of the styles requiring more than two columns of information (e.g.,
 `errorbars`) can be used with `splot`s or function `plot`s.  Neither `boxes`
 nor any of the `steps` styles can be used with `splot`s.  If an inappropriate
 style is specified, it will be changed to `points`.

 For 2-d data with more than two columns, `gnuplot` is picky about the allowed
 `errorbar` styles.  The `using` option on the `plot` command can be used to
 set up the correct columns for the style you want.  (In this discussion,
 "column" will be used to refer both to a column in the data file and an entry
 in the `using` list.)

 For three columns, only `xerrorbars`, `yerrorbars` (or `errorbars`), `boxes`,
 and `boxerrorbars` are allowed.  If another plot style is used, the style
 will be changed to `yerrorbars`.  The `boxerrorbars` style will calculate the
 boxwidth automatically.

 For four columns, only `xerrorbars`, `yerrorbars` (or `errorbars`),
 `xyerrorbars`, `boxxyerrorbars`, and `boxerrorbars` are allowed.  An illegal
 style will be changed to `yerrorbars`.

 Five-column data allow only the `boxerrorbars`, `financebars`, and
 `candlesticks` styles.  (The last two of these are primarily used for plots
 of financial prices.)  An illegal style will be changed to `boxerrorbars`
 before plotting.

 Six- and seven-column data only allow the `xyerrorbars` and `boxxyerrorbars`
 styles.  Illegal styles will be changed to `xyerrorbars` before plotting.

 For more information about error bars, please see `plot errorbars`.
4 boxerrorbars
?commands set style boxerrorbars
?set style boxerrorbars
?style boxerrorbars
?boxerrorbars
 The `boxerrorbars` style is only relevant to 2-d data plotting.  It is a
 combination of the `boxes` and `yerrorbars` styles.  The boxwidth will come
 from the fourth column if the y errors are in the form of "ydelta" and the
 boxwidth was not previously set equal to -2.0 (`set boxwidth -2.0`) or from
 the fifth column if the y errors are in the form of "ylow yhigh".  The
 special case  `boxwidth = -2.0` is for four-column data with y errors in the
 form "ylow yhigh".  In this case the boxwidth will be calculated so that each
 box touches the adjacent boxes.  The width will also be calculated in cases
 where three-column data are used.

 The box height is determined from the y error in the same way as it is for
 the `yerrorbars` style---either from y-ydelta to y+ydelta or from ylow to
 yhigh, depending on how many data columns are provided.
^<a href="http://www.nas.nasa.gov/~woo/gnuplot/errorbar/errorbar.html"> See Demo. </a>
4 boxes
?commands set style boxes
?commands set style bargraph
?set style boxes
?set style bargraph
?style boxes
?style bargraph
?boxes
?bargraph
 The `boxes` style is only relevant to 2-d plotting.  It draws a box centered
 about the given x coordinate from the x axis (not the graph border) to the
 given y coordinate.  The width of the box is obtained in one of three ways.
 If it is a data plot and the data file has a third column, this will be used
 to set the width of the box.  If not, if a width has been set using the `set
 boxwidth` command, this will be used.  If neither of these is available, the
 width of each box will be calculated automatically so that it touches the
 adjacent boxes.
4 boxxyerrorbars
?commands set style boxxyerrorbars
?set style boxxyerrorbars
?style boxxyerrorbars
?boxxyerrorbars
 The `boxxyerrorbars` style is only relevant to 2-d data plotting.  It is a
 combination of the `boxes` and `xyerrorbars` styles.

 The box width and height are determined from the x and y errors in the same
 way as they are for the `xyerrorbars` style---either from xlow to xhigh and
 from ylow to yhigh, or from x-xdelta to x+xdelta and from y-ydelta to
 y+ydelta , depending on how many data columns are provided.
4 candlesticks
?commands set style candlesticks
?set style candlesticks
?style candlesticks
?candlesticks
 The `candlesticks` style is only relevant for 2-d data plotting of financial
 data.  Five columns of data are required; in order, these should be the x
 coordinate (most likely a date) and the opening, low, high, and closing
 prices.  The symbol is an open rectangle, centered horizontally at the x
 coordinate and limited vertically by the opening and closing prices.  A
 vertical line segment at the x coordinate extends up from the top of the
 rectangle to the high price and another down to the low.  The width of the
 rectangle may be changed by `set bar`.  The symbol will be unchanged if the
 low and high prices are interchanged or if the opening and closing prices
 are interchanged.  See `set bar` and `financebars`.
^<a href="http://www.nas.nasa.gov/~woo/gnuplot/finance/finance.html"> See demos.</a>
4 dots
?commands set style dots
?set style dots
?style dots
?dots
 The `dots` style plots a tiny dot at each point; this is useful for scatter
 plots with many points.
4 financebars
?commands set style financebars
?set style financebars
?style financebars
?financebars
 The `financebars` style is only relevant for 2-d data plotting of financial
 data.  Five columns of data are required; in order, these should be the x
 coordinate (most likely a date) and the opening, low, high, and closing
 prices.  The symbol is a vertical line segment, located horizontally at the x
 coordinate and limited vertically by the high and low prices.  A horizontal
 tic on the left marks the opening price and one on the right marks the
 closing price.  The length of these tics may be changed by `set bar`.  The
 symbol will be unchanged if the high and low prices are interchanged.  See
 `set bar` and `candlesticks`.
^<a href="http://www.nas.nasa.gov/~woo/gnuplot/finance/finance.html"> See demos.</a>
4 fsteps
?commands set style fsteps
?set style fsteps
?style fsteps
?fsteps
 The `fsteps` style is only relevant to 2-d plotting.  It connects consecutive
 points with two line segments: the first from (x1,y1) to (x1,y2) and the
 second from (x1,y2) to (x2,y2).
^<a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/steps.html"> See demo. </a>
4 histeps
?commands set style histeps
?set style histeps
?style histeps
?histeps
 The `histeps` style is only relevant to 2-d plotting.  It is intended for
 plotting histograms.  Y-values are assumed to be centered at the x-values;
 the point at x1 is represented as a horizontal line from ((x0+x1)/2,y1) to
 ((x1+x2)/2,y1).  The lines representing the end points are extended so that
 the step is centered on at x.  Adjacent points are connected by a vertical
 line at their average x, that is, from ((x1+x2)/2,y1) to ((x1+x2)/2,y2).

 If `autoscale` is in effect, it selects the xrange from the data rather than
 the steps, so the end points will appear only half as wide as the others.
^<a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/steps.html"> See demo. </a>

 `histeps` is only a plotting style; `gnuplot` does not have the ability to
 create bins and determine their population from some data set.
4 impulses
?commands set style impulses
?set style impulses
?style impulses
?impulses
 The `impulses` style displays a vertical line from the x axis (not the graph
 border), or from the grid base for `splot`, to each point.
4 lines
?commands set style lines
?set style lines
?style lines
?lines
 The `lines` style connects adjacent points with straight line segments.
4 linespoints
?commands set style linespoints
?commands set style lp
?set style linespoints
?set style lp
?style linespoints
?style lp
?linespoints
?lp
 The `linespoints` style does both `lines` and `points`, that is, it draws a
 small symbol at each point and then connects adjacent points with straight
 line segments.  The command `set pointsize` may be used to change the size of
 the points.  See `set pointsize` for its usage.

 `linespoints` may be abbreviated `lp`.
4 points
?commands set style points
?set style points
?style points
?points
 The `points` style displays a small symbol at each point.  The command `set
 pointsize` may be used to change the size of the points.  See `set pointsize`
 for its usage.
4 steps
?commands set style steps
?set style steps
?style steps
?steps
 The `steps` style is only relevant to 2-d plotting.  It connects consecutive
 points with two line segments: the first from (x1,y1) to (x2,y1) and the
 second from (x2,y1) to (x2,y2).
^<a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/steps.html"> See demo. </a>
4 vector
?commands set style vector
?set style vector
?style vector
?vector
 The `vector` style draws a vector from (x,y) to (x+xdelta,y+ydelta).  Thus
 it requires four columns of data.  It also draws a small arrowhead at the
 end of the vector.

 The `vector` style is still experimental: it doesn't get clipped properly
 and other things may also be wrong with it.  Use it at your own risk.
4 xerrorbars
?commands set style xerrorbars
?set style xerrorbars
?style xerrorbars
?xerrorbars
 The `xerrorbars` style is only relevant to 2-d data plots.  `xerrorbars` is
 like `dots`, except that a horizontal error bar is also drawn.  At each point
 (x,y), a line is drawn from (xlow,y) to (xhigh,y) or from (x-xdelta,y) to
 (x+xdelta,y), depending on how many data columns are provided.  A tic mark
 is placed at the ends of the error bar (unless `set bar` is used---see `set
 bar` for details).
4 xyerrorbars
?commands set style xyerrorbars
?set style xyerrorbars
?style xyerrorbars
?xyerrorbars
 The `xyerrorbars` style is only relevant to 2-d data plots.  `xyerrorbars` is
 like `dots`, except that horizontal and vertical error bars are also drawn.
 At each point (x,y), lines are drawn from (x,y-ydelta) to (x,y+ydelta) and
 from (x-xdelta,y) to (x+xdelta,y) or from (x,ylow) to (x,yhigh) and from
 (xlow,y) to (xhigh,y), depending upon the number of data columns provided.  A
 tic mark is placed at the ends of the error bar (unless `set bar` is
 used---see `set bar` for details).

 If data are provided in an unsupported mixed form, the `using` filter on the
 `plot` command should be used to set up the appropriate form.  For example,
 if the data are of the form (x,y,xdelta,ylow,yhigh), then you can use

       plot 'data' using 1:2:($1-$3),($1+$3),4,5 with xyerrorbars
4 yerrorbars
?commands set style yerrorbars
?commands set style errorbars
?set style yerrorbars
?set style errorbars
?style yerrorbars
?style errorbars
?yerrorbars
?errorbars
 The `yerrorbars` (or `errorbars`) style is only relevant to 2-d data plots.
 `yerrorbars` is like `dots`, except that a vertical error bar is also drawn.
 At each point (x,y), a line is drawn from (x,y-ydelta) to (x,y+ydelta) or
 from (x,ylow) to (x,yhigh), depending on how many data columns are provided.
 A tic mark is placed at the ends of the error bar (unless `set bar` is
 used---see `set bar` for details).
^<a href="http://www.nas.nasa.gov/~woo/gnuplot/errorbar/errorbar.html"> See demo. </a>
3 surface
?commands set surface
?commands set nosurface
?commands show surface
?set surface
?set nosurface
?show surface
?surface
?nosurface
 The command `set surface` controls the display of surfaces by `splot`.

 Syntax:
       set surface
       set nosurface
       show surface

 The surface is drawn with the style specifed by `with`, or else the
 appropriate style, data or function.

 Whenever `set nosurface` is issued, `splot` will not draw points or lines
 corresponding to the function or data file points.  Contours may be still be
 drawn on the surface, depending on the `set contour` option. `set nosurface;
 set contour base` is useful for displaying contours on the grid base.  See
 also `set contour`.
^ <h2> Terminal Types </h2>
3 terminal
?commands set terminal
?commands show terminal
?set terminal
?set term
?show terminal
?terminal
?term
 `gnuplot` supports many different graphics devices.  Use `set terminal` to
 tell `gnuplot` what kind of output to generate. Use `set output` to redirect
 that output to a file or device.

 Syntax:
       set terminal {<terminal-type>}
       show terminal

 If <terminal-type> is omitted, `gnuplot` will list the available terminal
 types.  <terminal-type> may be abbreviated.

 If both `set terminal` and `set output` are used together, it is safest to
 give `set terminal` first, because some terminals set a flag which is needed
 in some operating systems.

 Several terminals have additional options.  For example, see `dumb`,
 `iris4d`, `hpljii` or `postscript`.

 This document may describe drivers that are not available to you because they
 were not installed, or it may not describe all the drivers that are available
 to you, depending on its output format.
<4 -- all terminal stuff is pulled from the .trm files
3 tics
?commands set tics
?commands show tics
?set tics
?show tics
?tics
 The `set tics` command can be used to change the tics to be drawn outwards.

 Syntax:
       set tics {<direction>}
       show tics

 where <direction> may be `in` (the default) or `out`.

 See also `set xtics` for more control of major (labelled) tic marks and `set
 mxtics` for control of minor tic marks.
3 ticslevel
?commands set ticslevel
?commands show ticslevel
?set ticslevel
?show ticslevel
?ticslevel
 Using `splot`, one can adjust the relative height of the vertical (Z) axis
 using `set ticslevel`.  The numeric argument provided specifies the location
 of the bottom of the scale (as a fraction of the z-range) above the xy-plane.
 The default value is 0.5.  Negative values are permitted, but tic labels on
 the three axes may overlap.

 To place the xy-plane at a position 'pos' on the z-axis, `ticslevel` should
 be set equal to  (pos - zmin) / (zmin - zmax).

 Syntax:
       set ticslevel {<level>}
       show tics

 See also `set view`.
3 ticscale
?commands set ticscale
?commands show ticscale
?set ticscale
?show ticscale
?ticscale
 The size of the tic marks can be adjusted with `set ticscale`.

 Syntax:
       set ticscale {<major> {<minor>}}
       show tics

 If <minor> is not specified, it is 0.5*<major>.  The default size is 1.0 for
 major tics and 0.5 for minor tics.  Note that it is possible to have the tic
 marks pointing outward by specifying a negative size.
3 timestamp
?commands set timestamp
?commands set time
?commands set notimestamp
?commands show timestamp
?set timestamp
?set time
?set notimestamp
?show timestamp
?timestamp
?notimestamp
 The command `set timestamp` places the time and date of the plot in the left
 margin.

 Syntax:
       set timestamp {"<format>"} {top|bottom} {{no}rotate}
                     {<xoff>}{,<yoff>} {"<font>"}
       set notimestamp
       show timestamp

 The format string allows you to choose the format used to write the date and
 time.  Its default value is what asctime() uses: "%a %b %d %H:%M:%S %Y"
 (weekday, month name, day of the month, hours, minutes, seconds, four-digit
 year).  With `top` or `bottom` you can place the timestamp at the top or
 bottom of the left margin (default: bottom).  `rotate` lets you write the
 timestamp vertically, if your terminal supports vertical text.  The constants
 <xoff> and <off> are offsets from the default position given in character
 screen coordinates.  <font> is used to specify the font with which the time
 is to be written.

 The abbreviation `time` may be used in place of `timestamp`.

 Example:
       set timestamp "%d/%m/%y %H:%M" 80,-2 "Helvetica"

 See `set timefmt` for more information about time format strings.
3 timefmt
?commands set timefmt
?commands show timefmt
?set timefmt
?show timefmt
?timefmt
 This command applies to timeseries where data are composed of dates/times.
 It has no meaning unless the command `set xdata time` is given also.

 Syntax:
       set timefmt "<format string>"
       show timefmt

 The string argument tells `gnuplot` how to read timedata from the datafile.
 The valid formats are:

@start table - first is interactive cleartext form
       Format       Explanation
       %d           day of the month, 1--31
       %m           month of the year, 1--12
       %y           year, 0--99
       %Y           year, 4-digit
       %j           day of the year, 1--365
       %H           hour, 0--24
       %M           minute, 0--60
       %S           second, 0--60
       %b           three-character abbreviation of the name of the month
       %B           name of the month
#\begin{tabular}{|cl|} \hline
#\multicolumn{2}{|c|}{Time Series timedata Format Specifiers}\\
#\hline \hline
#Format & Explanation \\ \hline
#\verb@%d@ & day of the month, 1--31 \\
#\verb@%m@ & month of the year, 1--12 \\
#\verb@%y@ & year, 0--99 \\
#\verb@%Y@ & year, 4-digit \\
#\verb@%j@ & day of the year, 1--365 \\
#\verb@%H@ & hour, 0--24 \\
#\verb@%M@ & minute, 0--60 \\
#\verb@%S@ & second, 0--60 \\
#\verb@%b@ & three-character abbreviation of the name of the month \\
#\verb@%B@ & name of the month \\
%c l .
%Format@Explanation
%_
%%d@day of the month, 1--31
%%m@month of the year, 1--12
%%y@year, 0--99
%%Y@year, 4-digit
%%j@day of the year, 1--365
%%H@hour, 0--24
%%M@minute, 0--60
%%S@second, 0--60
%%b@three-character abbreviation of the name of the month
%%B@name of the month
%_
@end table
 Any character is allowed in the string, but must match exactly.  \t (tab) is
 recognized.  Backslash-octals (\nnn) are converted to char.  If there is no
 separating character between the time/date elements, then %d, %m, %y, %H, %M
 and %S read two digits each, %Y reads four digits and %j reads three digits.
 %b requires three characters, and %B requires as many as it needs.

 Spaces are treated slightly differently.  A space in the string stands for
 zero or more whitespace characters in the file.  That is, "%H %M" can be used
 to read "1220" and "12     20" as well as "12 20".

 Each set of non-blank characters in the timedata counts as one column in the
 `using n:n` specification.  Thus `11:11  25/12/76  21.0` consists of three
 columns.  To avoid confusion, `gnuplot` requires that you provide a complete
 `using` specification if your file contains timedata.

 Since `gnuplot` cannot read non-numerical text, if the date format includes
 the day or month in words, the format string must exclude this text.  But
 it can still be printed with the "%a", "%A", "%b", or "%B" specifier: see
 `set format` for more details about these and other options for printing
 timedata.  (`gnuplot` will determine the proper month and weekday from the
 numerical values.)

 See also `set xdata` and `Time/date` for more information.

 Example:
       set timefmt "%d/%m/%Y\t%H:%M"
 tells `gnuplot` to read date and time separated by tab.  (But look closely at
 your data---what began as a tab may have been converted to spaces somewhere
 along the line; the format string must match what is actually in the file.)
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/timedat.html"> Time Data Demo </a>
3 title
?commands set title
?commands show title
?set title
?show title
?title
 The `set title` command produces a plot title that is centered at the top of
 the plot.  `set title` is a special case of `set label`.

 Syntax:
       set title {"<title-text>"} {<xoff>}{,<yoff>} {"<font>,{<size>}"}
       show title

 Specifying constants <xoff> or <yoff> as optional offsets for the title will
 move the title <xoff> or <yoff> character screen coordinates (not graph
 coordinates).  For example, "`set title ,-1`" will change only the y offset
 of the title, moving the title down by roughly the height of one character.

 <font> is used to specify the font with which the title is to be written;
 the units of the font <size> depend upon which terminal is used.

 `set title` with no parameters clears the title.

 See `syntax` for details about the processing of backslash sequences and
 the distinction between single- and double-quotes.
3 tmargin
?commands set tmargin
?set tmargin
?tmargin
 The command `set tmargin` sets the size of the top margin.  Please see
 `set margin` for details.
3 trange
?commands set trange
?commands show trange
?set trange
?show trange
?trange
 The `set trange` command sets the parametric range used to compute x and y
 values when in parametric or polar modes.  Please see `set xrange` for
 details.
3 urange
?commands set urange
?commands show urange
?set urange
?show urange
?urange
 The `set urange` and `set vrange` commands set the parametric ranges used
 to compute x, y, and z values when in `splot` parametric mode.  Please see
 `set xrange` for details.
3 variables
?commands show variables
?show variables
 The `show variables` command lists all user-defined variables and their
 values.

 Syntax:
       show variables
3 version
?show version
 The `show version` command lists the version of gnuplot being run, its last
 modification date, the copyright holders, and email addresses for the FAQ,
 the info-gnuplot mailing list, and reporting bugs--in short, the information
 listed on the screen when the program is invoked interactively.

 Syntax:
       show version {long}

 When the `long` option is given, it also lists the operating system, the
 compilation options used when `gnuplot` was installed, the location of the
 help file, and (again) the useful email addresses.
3 view
?commands set view
?commands show view
?set view
?show view
?view
 The `set view` command sets the viewing angle for `splot`s.  It controls how
 the 3-d coordinates of the plot are mapped into the 2-d screen space.  It
 provides controls for both rotation and scaling of the plotted data, but
 supports orthographic projections only.

 Syntax:
       set view <rot_x> {,{<rot_z>}{,{<scale>}{,<scale_z>}}}
       show view

 where <rot_x> and <rot_z> control the rotation angles (in degrees) in a
 virtual 3-d coordinate system aligned with the screen such that initially
 (that is, before the rotations are performed) the screen horizontal axis is
 x, screen vertical axis is y, and the axis perpendicular to the screen is z.
 The first rotation applied is <rot_x> around the x axis.  The second rotation
 applied is <rot_z> around the new z axis.

 <rot_x> is bounded to the [0:180] range with a default of 60 degrees, while
 <rot_z> is bounded to the [0:360] range with a default of 30 degrees.
 <scale> controls the scaling of the entire `splot`, while <scale_z> scales
 the z axis only.  Both scales default to 1.0.

 Examples:
       set view 60, 30, 1, 1
       set view ,,0.5

 The first sets all the four default values.  The second changes only scale,
 to 0.5.

 See also `set ticslevel`.
3 vrange
?commands set vrange
?commands show vrange
?set vrange
?show vrange
?vrange
 The `set urange` and `set vrange` commands set the parametric ranges used
 to compute x, y, and z values when in `splot` parametric mode.  Please see
 `set xrange` for details.
3 x2data
?commands set x2data
?commands show x2data
?set x2data
?show x2data
?x2data
 The `set x2data` command sets data on the x2 (top) axis to timeseries
 (dates/times).  Please see `set xdata`.
3 x2dtics
?commands set x2dtics
?commands set nox2dtics
?commands show x2dtics
?set x2dtics
?set nox2dtics
?show x2dtics
?x2dtics
?nox2dtics
 The `set x2dtics` command changes tics on the x2 (top) axis to days of the
 week.  Please see `set xdtics` for details.
3 x2label
?commands set x2label
?commands show x2label
?set x2label
?show x2label
?x2label
 The `set x2label` command sets the label for the x2 (top) axis.  Please see
 `set xlabel`.
3 x2mtics
?commands set x2mtics
?commands set nox2mtics
?commands show x2mtics
?set x2mtics
?set nox2mtics
?show x2mtics
?x2mtics
?nox2mtics
 The `set x2mtics` command changes tics on the x2 (top) axis to months of the
 year.  Please see `set xmtics` for details.
3 x2range
?commands set x2range
?commands show x2range
?set x2range
?show x2range
?x2range
 The `set x2range` command sets the horizontal range that will be displayed on
 the x2 (top) axis.  Please see `set xrange` for details.
3 x2tics
?commands set x2tics
?commands set nox2tics
?commands show x2tics
?set x2tics
?set nox2tics
?show x2tics
?x2tics
?nox2tics
 The `set x2tics` command controls major (labelled) tics on the x2 (top) axis.
 Please see `set xtics` for details.
3 x2zeroaxis
?commands set x2zeroaxis
?commands set nox2zeroaxis
?commands show x2zeroaxis
?set x2zeroaxis
?set nox2zeroaxis
?show x2zeroaxis
?x2zeroaxis
?nox2zeroaxis
 The `set x2zeroaxis` command draws a line at the origin of the x2 (top) axis
 (y2 = 0).  For details, please see
 `set zeroaxis`.
3 xdata
?commands set xdata
?commands show xdata
?set xdata
?show xdata
?xdata
 This command sets the datatype on the x axis to time/date.  A similar command
 does the same thing for each of the other axes.

 Syntax:
       set xdata {time}
       show xdata

 The same syntax applies to `ydata`, `zdata`, `x2data` and `y2data`.

 The `time` option signals that the datatype is indeed time/date.  If the
 option is not specified, the datatype reverts to normal.

 See `set timefmt` to tell `gnuplot` how to read date or time data.  The
 time/date is converted to seconds from start of the century.  There is
 currently only one timefmt, which implies that all the time/date columns must
 confirm to this format.  Specification of ranges should be supplied as quoted
 strings according to this format to avoid interpretation of the time/date as
 an expression.

 The function 'strftime' (type "man strftime" on unix to look it up) is used
 to print tic-mark labels.  `gnuplot` tries to figure out a reasonable format
 for this  unless the `set format x "string"` has supplied something that does
 not look like a decimal format (more than one '%' or neither %f nor %g).

 See also `Time/date` for more information.
3 xdtics
?commands set xdtics
?commands set noxdtics
?commands show xdtics
?set xdtics
?set noxdtics
?show xdtics
?xdtics
?noxdtics
 The `set xdtics` commands converts the x-axis tic marks to days of the week
 where 0=Sun and 6=Sat.  Overflows are converted modulo 7 to dates.  `set
 noxdtics` returns the labels to their default values.  Similar commands do
 the same things for the other axes.

 Syntax:
       set xdtics
       set noxdtics
       show xdtics

 The same syntax applies to `ydtics`, `zdtics`, `x2dtics` and `y2dtics`.

 See also the `set format` command.
3 xlabel
?commands set xlabel
?commands show xlabel
?set xlabel
?show xlabel
?xlabel
 The `set xlabel` command sets the x axis label.  Similar commands set labels
 on the other axes.

 Syntax:
       set xlabel {"<label>"} {<xoff>}{,<yoff>} {"<font>{,<size>}"}
       show xlabel

 The same syntax applies to `x2label`, `ylabel`, `y2label` and `zlabel`.

 Specifying the constants <xoff> or <yoff> as optional offsets for a label
 will move it <xoff> or <yoff> character widths or heights.  For example,
 "` set xlabel -1`" will change only the x offset of the xlabel, moving the
 label roughly one character width to the left.   The size of a character
 depends on both the font and the terminal.

 <font> is used to specify the font in which the label is written; the units
 of the font <size> depend upon which terminal is used.

 To clear a label, put no options on the command line, e.g., "`set y2label`".

 The default positions of the axis labels are as follows:

 xlabel:  The x-axis label is centered below the bottom axis.

 ylabel:  The position of the y-axis label depends on the terminal, and can be
 one of the following three positions:

 1. Horizontal text flushed left at the top left of the plot.  Terminals that
 cannot rotate text will probably use this method.  If `set x2tics` is also
 in use, the ylabel may overwrite the left-most x2tic label.  This may be
 remedied by adjusting the ylabel position or the left margin.

 2. Vertical text centered vertically at the left of the plot.  Terminals
 that can rotate text will probably use this method.

 3. Horizontal text centered vertically at the left of the plot.  The EEPIC,
 LaTeX and TPIC drivers use this method.  The user must insert line breaks
 using \\ to prevent the ylabel from overwriting the plot.  To produce a
 vertical row of characters, add \\ between every printing character (but this
 is ugly).

 zlabel: The z-axis label is centered along the z axis and placed in the space
 above the grid level.

 y2label: The y2-axis label is placed to the right of the y2 axis.  The
 position is terminal-dependent in the same manner as is the y-axis label.

 x2label: The x2-axis label is placed above the top axis but below the plot
 title.  It is also possible to create an x2-axis label by using new-line
 characters to make a multi-line plot title, e.g.,

       set title "This is the title\n\nThis is the x2label"

 Note that double quotes must be used.  The same font will be used for both
 lines, of course.

 If you are not satisfied with the default position of an axis label, use `set
 label` instead--that command gives you much more control over where text is
 placed.

 Please see `set syntax` for further information about backslash processing
 and the difference between single- and double-quoted strings.
3 xmtics
?commands set xmtics
?commands set noxmtics
?commands show xmtics
?set xmtics
?set noxmtics
?show xmtics
?xmtics
?noxmtics
 The `set xmtics` commands converts the x-axis tic marks to months of the
 year where 1=Jan and 12=Dec.  Overflows are converted modulo 12 to months.
 The tics are returned to their default labels by `set noxmtics`.  Similar
 commands perform the same duties for the other axes.

 Syntax:
       set xmtics
       set noxmtics
       show xmtics

 The same syntax applies to `x2mtics`, `ymtics`, `y2mtics`, and `zmtics`.

 See also the `set format` command.
3 xrange
?commands set xrange
?commands show xrange
?set xrange
?show xrange
?xrange
 The `set xrange` command sets the horizontal range that will be displayed.
 A similar command exists for each of the other axes, as well as for the
 polar radius r and the parametric variables t, u, and v.

 Syntax:
       set xrange [{{<min>}:{<max>}}] {{no}reverse} {{no}writeback}
       show xrange

 where <min> and <max> terms are constants, expressions or an asterisk to set
 autoscaling.  If the data are time/date, you must give the range as a quoted
 string according to the `set timefmt` format.  Any value omitted will not be
 changed.

 The same syntax applies to `yrange`, `zrange`, `x2range`, `y2range`,
 `rrange`, `trange`, `urange` and `vrange`.

 The `reverse` option reverses the direction of the axis, e.g., `set xrange
 [0:1] reverse` will produce an axis with 1 on the left and 0 on the right.
 This is identical to the axis produced by `set xrange [1:0]`, of course.
 `reverse` is intended primarily for use with `autoscale`.

 The `writeback` option essentially saves the range found by `autoscale` in
 the buffers that would be filled by `set xrange`.  This is useful if you wish
 to plot several functions together but have the range determined by only
 some of them.  The `writeback` operation is performed during the `plot`
 execution, so it must be specified before that command.  For example,

       set xrange [-10:10]
       set yrange [] writeback
       plot sin(x)
       set noautoscale y
       replot x/2

 results in a yrange of [-1:1] as found only from the range of sin(x); the
 [-5:5] range of x/2 is ignored.  Executing `show yrange` after each command
 in the above example should help you understand what is going on.

 In 2-d, `xrange` and `yrange` determine the extent of the axes, `trange`
 determines the range of the parametric variable in parametric mode or the
 range of the angle in polar mode.  Similarly in parametric 3-d, `xrange`,
 `yrange`, and `zrange` govern the axes and `urange` and `vrange` govern the
 parametric variables.

 In polar mode, `rrange` determines the radial range plotted.  <rmin> acts as
 an additive constant to the radius, whereas <rmax> acts as a clip to the
 radius---no point with radius greater than <rmax> will be plotted.  `xrange`
 and `yrange` are affected---the ranges can be set as if the graph was of
 r(t)-rmin, with rmin added to all the labels.

 Any range may be partially or totally autoscaled, although it may not make
 sense to autoscale a parametric variable unless it is plotted with data.

 Ranges may also be specified on the `plot` command line.  A range given on
 the plot line will be used for that single `plot` command; a range given by
 a `set` command will be used for all subsequent plots that do not specify
 their own ranges.  The same holds true for `splot`.

 Examples:

 To set the xrange to the default:
       set xrange [-10:10]

 To set the yrange to increase downwards:
       set yrange [10:-10]

 To change zmax to 10 without affecting zmin (which may still be autoscaled):
       set zrange [:10]

 To autoscale xmin while leaving xmax unchanged:
       set xrange [*:]
3 xtics
?commands set xtics
?commands set noxtics
?commands show xtics
?set xtics
?set noxtics
?show xtics
?xtics
?noxtics
 Fine control of the major (labelled) tics on the x axis is possible with the
 `set xtics` command.  The tics may be turned off with the `set noxtics`
 command, and may be turned on (the default state) with `set xtics`.  Similar
 commands control the major tics on the y, z, x2 and y2 axes.

 Syntax:
       set xtics {axis | border} {{no}mirror} {{no}rotate}
                 {  autofreq
                  | <incr>
                  | <start>, <incr> {,<end>}
                  | ({"<label>"} <pos> {,{"<label>"} <pos>}...) }
       set noxtics
       show xtics

 The same syntax applies to `ytics`, `ztics`, `x2tics` and `y2tics`.

 `axis` or `border` tells `gnuplot` to put the tics (both the tics themselves
 and the accompanying labels) along the axis or the border, respectively.  If
 the axis is very close to the border, the `axis` option can result in tic
 labels overwriting other text written in the margin.

 `mirror` tells `gnuplot` to put unlabelled tics at the same positions on the
 opposite border.  `nomirror` does what you think it does.

 `rotate` asks `gnuplot` to rotate the text through 90 degrees, which will be
 done if the terminal driver in use supports text rotation.  `norotate`
 cancels this.

 The defaults are `border mirror norotate` for tics on the x and y axes, and
 `border nomirror norotate` for tics on the x2 and y2 axes.  For the z axis,
 the the `{axis | border}` option is not available and the default is
 `nomirror`.  If you do want to mirror the z-axis tics, you might want to
 create a bit more room for them with `set border`.

 `set xtics` with no options restores the default border or axis if xtics are
 being displayed;  otherwise it has no effect.  Any previously specified tic
 frequency or position {and labels} are retained.

 Positions of the tics are calculated automatically by default or if the
 `autofreq` option is given; otherwise they may be specified in either of
 two forms:

 The implicit <start>, <incr>, <end> form specifies that a series of tics will
 be plotted on the axis between the values <start> and <end> with an increment
 of <incr>.  If <end> is not given, it is assumed to be infinity.  The
 increment may be negative.  If neither <start> nor <end> is given, <start> is
 assumed to be negative infinity, <end> is assumed to be positive infinity,
 and the tics will be drawn at integral multiples of <step>.  If the axis is
 logarithmic, the increment will be used as a multiplicative factor.

 Examples:

 Make tics at 0, 0.5, 1, 1.5, ..., 9.5, 10.
       set xtics 0,.5,10

 Make tics at ..., -10, -5, 0, 5, 10, ...
       set xtics 5

 Make tics at 1, 100, 1e4, 1e6, 1e8.
       set logscale x; set xtics 1,100,10e8

 The explicit ("<label>" <pos>, ...) form allows arbitrary tic positions or
 non-numeric tic labels.  A set of tics is a set of positions, each with its
 own optional label.  Note that the label is a string enclosed by quotes.  It
 may be a constant string, such as "hello", may contain formatting information
 for converting the position into its label, such as "%3f clients", or may be
 empty, "".  See `set format` for more information.  If no string is given,
 the default label (numerical) is used.  In this form, the tics do not need to
 be listed in numerical order.

 Examples:
       set xtics ("low" 0, "medium" 50, "high" 100)
       set xtics (1,2,4,8,16,32,64,128,256,512,1024)
       set ytics ("bottom" 0, "" 10, "top" 20)

 In the second example, all tics are labelled.  In the third, only the end
 tics are labelled.

 However they are specified, tics will only be plotted when in range.

 Format (or omission) of the tic labels is controlled by `set format`, unless
 the explicit text of a labels is included in the `set xtic (`<label>`)` form.

 Minor (unlabelled) tics can be added by the `set mxtics` command.

 In case of timeseries data, position values must be given as quoted dates
 or times according to the format `timefmt`.  If the <start>, <incr>, <end>
 form is used, <start> and <end> must be given according to `timefmt`, but
 <incr> must be in seconds.  Times will be written out according to the format
 given on `set format`, however.

 Examples:
       set xdata time
       set timefmt "%d/%m"
       set format x "%b %d"
       set xrange ["01/12":"06/12"]
       set xtics "01/12", 172800, "05/12"

       set xdata time
       set timefmt "%d/%m"
       set format x "%b %d"
       set xrange ["01/12":"06/12"]
       set xtics ("01/12", "" "03/12", "05/12")
 Both of these will produce tics "Dec 1", "Dec 3", and "Dec 5", but in the
 second example the tic at "Dec 3" will be unlabelled.

3 xzeroaxis
?commands set xzeroaxis
?commands set noxzeroaxis
?commands show xzeroaxis
?set xzeroaxis
?set noxzeroaxis
?show xzeroaxis
?xzeroaxis
?noxzeroaxis
 The `set xzeroaxis` command draws a line at y = 0.  For details, please see
 `set zeroaxis`.
3 y2data
?commands set y2data
?commands show y2data
?set y2data
?show y2data
?y2data
 The `set y2data` command sets y2 (right-hand) axis data to timeseries
 (dates/times).  Please see `set xdata`.
3 y2dtics
?commands set y2dtics
?commands set noy2dtics
?set y2dtics
?set noy2dtics
?show y2dtics
?y2dtics
?noy2dtics
 The `set y2dtics` command changes tics on the y2 (right-hand) axis to days of
 the week.  Please see `set xdtics` for details.
3 y2label
?commands set y2label
?commands show y2label
?set y2label
?show y2label
?y2label
 The `set y2dtics` command sets the label for the y2 (right-hand) axis.
 Please see `set xlabel`.
3 y2mtics
?commands set y2mtics
?commands set noy2mtics
?commands show y2mtics
?set y2mtics
?set noy2mtics
?show y2mtics
?y2mtics
?noy2mtics
 The `set y2mtics` command changes tics on the y2 (right-hand) axis to months
 of the year.  Please see `set xmtics` for details.
3 y2range
?commands set y2range
?commands show y2range
?set y2range
?show y2range
?y2range
 The `set y2range` command sets the vertical range that will be displayed on
 the y2 (right-hand) axis.  Please see `set xrange` for details.
3 y2tics
?commands set y2tics
?commands set noy2tics
?commands show y2tics
?set y2tics
?set noy2tics
?show y2tics
?y2tics
?noy2tics
 The `set y2tics` command controls major (labelled) tics on the y2 (right-hand)
 axis.  Please see `set xtics` for details.
3 y2zeroaxis
?commands set y2zeroaxis
?commands set noy2zeroaxis
?commands show y2zeroaxis
?set y2zeroaxis
?set noy2zeroaxis
?show y2zeroaxis
?y2zeroaxis
?noy2zeroaxis
 The `set y2zeroaxis` command draws a line at the origin of the y2 (right-hand)
 axis (x2 = 0).  For details, please see `set zeroaxis`.
3 ydata
?commands set ydata
?commands show ydata
?set ydata
?show ydata
?ydata
 Sets y-axis data to timeseries (dates/times).  Please see `set xdata`.
3 ydtics
?commands set ydtics
?commands set noydtics
?commands show ydtics
?set ydtics
?set noydtics
?show ydtics
?ydtics
?noydtics
 The `set ydtics` command changes tics on the y axis to days of the week.
 Please see `set xdtics` for details.
3 ylabel
?commands set ylabel
?commands show ylabel
?set ylabel
?show ylabel
?ylabel
 This command sets the label for the y axis.  Please see `set xlabel`.
3 ymtics
?commands set ymtics
?commands set noymtics
?commands show ymtics
?set ymtics
?set noymtics
?show ymtics
?ymtics
?noymtics
 The `set ymtics` command changes tics on the y axis to months of the year.
 Please see `set xmtics` for details.
3 yrange
?commands set yrange
?commands show yrange
?set yrange
?show yrange
?yrange
 The `set yrange` command sets the vertical range that will be displayed on
 the y axis.  Please see `set xrange` for details.
3 ytics
?commands set ytics
?commands set noytics
?commands show ytics
?set ytics
?set noytics
?show ytics
?ytics
?noytics
 The `set ytics` command controls major (labelled) tics on the y axis.
 Please see `set xtics` for details.
3 yzeroaxis
?commands set yzeroaxis
?commands set noyzeroaxis
?commands show yzeroaxis
?set yzeroaxis
?set noyzeroaxis
?show yzeroaxis
?yzeroaxis
?noyzeroaxis
 The `set yzeroaxis` command draws a line at x = 0.  For details, please see
 `set zeroaxis`.
3 zdata
?commands set zdata
?commands show zdata
?set zdata
?show zdata
?zdata
 Set zaxis date to timeseries (dates/times).  Please see `set xdata`.
3 zdtics
?commands set zdtics
?commands set nozdtics
?commands show zdtics
?set zdtics
?set nozdtics
?show zdtics
?zdtics
?nozdtics
 The `set zdtics` command changes tics on the z axis to days of the week.
 Please see `set xdtics` for details.
3 zero
?commands set zero
?commands show zero
?set zero
?show zero
?zero
 The `zero` value is the default threshold for values approaching 0.0.

 Syntax:
       set zero <expression>
       show zero

 `gnuplot` will not plot a point if its imaginary part is greater in magnitude
 than the `zero` threshold.  This threshold is also used in various other
 parts of `gnuplot` as a (crude) numerical-error threshold.  The default
 `zero` value is 1e-8.  `zero` values larger than 1e-3 (the reciprocal of the
 number of pixels in a typical bitmap display) should probably be avoided, but
 it is not unreasonable to set `zero` to 0.0.
3 zeroaxis
?commands set zeroaxis
?commands set nozeroaxis
?commands show zeroaxis
?set zeroaxis
?set nozeroaxis
?show zeroaxis
?zeroaxis
?nozeroaxis
 The x axis may be drawn by `set xzeroaxis` and removed by `set noxzeroaxis`.
 Similar commands behave similarly for the y, x2, and y2 axes.

 Syntax:
       set {x|x2|y|y2|}zeroaxis { {linestyle | ls <line_style>}
                                  | { linetype | lt <line_type>}
                                    { linewidth | lw <line_width>}}
       set no{x|x2|y|y2|}zeroaxis
       show {x|y|}zeroaxis


 By default, these options are off.  The selected zero axis is drawn
 with a line of type <line_type> and width <line_width> (if supported
 by the terminal driver currently in use), or a user-defined style
 <line_style>.

 If no linetype is specified, any zero axes selected will be drawn
 using the axis linetype (linetype 0).

 `set zeroaxis l` is equivalent to `set xzeroaxis l; set yzeroaxis l`. `set
 nozeroaxis` is equivalent to `set noxzeroaxis; set noyzeroaxis`.
3 zlabel
?commands set zlabel
?commands show zlabel
?set zlabel
?show zlabel
?zlabel
 This command sets the label for the z axis.  Please see `set xlabel`.
3 zmtics
?commands set zmtics
?commands set nozmtics
?commands show zmtics
?set zmtics
?set nozmtics
?show zmtics
?zmtics
?nozmtics
 The `set zmtics` command changes tics on the z axis to months of the year.
 Please see `set xmtics` for details.
3 zrange
?commands set zrange
?commands show zrange
?set zrange
?show zrange
?zrange
 The `set zrange` command sets the range that will be displayed on the z axis.
 The zrange is used only by `splot` and is ignored by `plot`.  Please see `set
 xrange` for details.
3 ztics
?commands set ztics
?commands set noztics
?commands show ztics
?set ztics
?set noztics
?show ztics
?ztics
?noztics
 The `set ztics` command controls major (labelled) tics on the z axis.
 Please see `set xtics` for details.
2 shell
?commands shell
?shell
 The `shell` command spawns an interactive shell.  To return to `gnuplot`,
 type `logout` if using VMS, `exit` or the END-OF-FILE character if using
 Unix, `endcli` if using AmigaOS, or `exit` if using MS-DOS or OS/2.

 A single shell command may be spawned by preceding it with the ! character
 ($ if using VMS) at the beginning of a command line.  Control will return
 immediately to `gnuplot` after this command is executed.  For example, in
 Unix, AmigaOS, MS-DOS or OS/2,

       ! dir

 prints a directory listing and then returns to `gnuplot`.

 On an Atari, the `!` command first checks whether a shell is already loaded
 and uses it, if available.  This is practical if `gnuplot` is run from
 `gulam`, for example.
2 splot
?commands splot
?splot
 `splot` is the command for drawing 3-d plots (well, actually projections on
 a 2-d surface, but you knew that).  It can create a plot from functions or
 a data file in a manner very similar to the `plot` command.

 See `plot` for features common to the `plot` command; only differences are
 discussed in detail here.  Note specifically that the `binary` and `matrix`
 options (discussed under "datafile-modifiers") are not available for `plot`.

 Syntax:
       splot {<ranges>}
             <function> | "<datafile>" {datafile-modifiers}}
             {<title-spec>} {with <style>}
             {, {definitions,} <function> ...}

 where either a <function> or the name of a data file enclosed in quotes is
 supplied.  The function can be a mathematical expression, or a triple of
 mathematical expressions in parametric mode.

 By default `splot` draws the xy plane completely below the plotted data.
 The offset between the lowest ztic and the xy plane can be changed by `set
 ticslevel`.  The orientation of a `splot` projection is controlled by
 `set view`.  See `set view` and `set ticslevel` for more information.

 The syntax for setting ranges on the `splot` command is the same as for
 `plot`.  In non-parametric mode, the order in which ranges must be given is
 `xrange`, `yrange`, and `zrange`.  In parametric mode, the order is `urange`,
 `vrange`, `xrange`, `yrange`, and `zrange`.

 The `title` option is the same as in `plot`.  The operation of `with` is also
 the same as in `plot`, except that the plotting styles available to `splot`
 are limited to `lines`, `points`, `linespoints`, `dots`, and `impulses`;  the
 error-bar capabilities of `plot` are not available for `splot`.

 The datafile options have more differences.
3 data-file
?commands splot datafile
?splot datafile
?splot data-file
 As for `plot`, discrete data contained in a file can be displayed by
 specifying the name of the data file, enclosed in quotes,  on the `splot`
 command line.

 Syntax:
       splot '<file_name>' {binary | matrix}
                           {index <index list>}
                           {every <every list>}
                           {using <using list>}

 The special filenames `""` and `"-"` are permitted, as in `plot`.

 In brief, `binary` and `matrix` indicate that the the data are in a special
 form, `index` selects which data sets in a multi-data-set file are to be
 plotted, `every` specifies which datalines (subsets) within a single data
 set are to be plotted, and `using` determines how the columns within a single
 record are to be interpreted.

 The options `index` and `every` behave the same way as with `plot`;  `using`
 does so also, except that the `using` list must provide three entries
 instead of two.

 The `plot` options `thru` and `smooth` are not available for `splot`, but
 `cntrparams` and `dgrid3d` provide limited smoothing cabilities.

 Data file organization is essentially the same as for `plot`, except that
 each point is an (x,y,z) triple.  If only a single value is provided, it
 will be used for z, the datablock number will be used for y, and the index
 of the data point in the datablock will be used for x.  If two values are
 provided, `gnuplot` gives you an error message.  Three values are interpreted
 as an (x,y,z) triple.  Additional values are generally used as errors, which
 can be used by `fit`.

 Single blank records separate datablocks in a `splot` datafile; `splot`
 treats datablocks as the equivalent of function y-isolines.  No line will
 join points separated by a blank record.  If all datablocks contain the same
 number of points, `gnuplot` will draw cross-isolines between datablocks,
 connecting corresponding points.  This is termed "grid data", and is required
 for drawing a surface, for contouring (`set contour`) and hidden-line removal
 (`set hidden3d`). See also `splot grid data`

 It is no longer necessary to specify `parametric` mode for three-column
 `splot`s.
4 binary
?commands splot datafile binary
?splot datafile binary
?splot binary
?data-file binary
?datafile binary
?binary
?binary data
?binary files
 `splot` can read binary files written with a specific format (and on a
 system with a compatible binary file representation.)

 In previous versions, `gnuplot` dynamically detected binary data files.  It
 is now necessary to specify the keyword `binary` directly after the filename.

 Single precision floats are stored in a binary file as follows:

       <N+1>  <y0>   <y1>   <y2>  ...  <yN>
        <x0> <z0,0> <z0,1> <z0,2> ... <z0,N>
        <x1> <z1,0> <z1,1> <z1,2> ... <z1,N>
         :      :      :      :   ...    :

 which are converted into triplets:
       <x0> <y0> <z0,0>
       <x0> <y1> <z0,1>
       <x0> <y2> <z0,2>
        :    :     :
       <x0> <yN> <z0,N>

       <x1> <y0> <z1,0>
       <x1> <y1> <z1,1>
        :    :     :

 These triplets are then converted into `gnuplot` iso-curves and then
 `gnuplot` proceeds in the usual manner to do the rest of the plotting.

 A collection of matrix and vector manipulation routines (in C) is provided
 in `binary.c`.  The routine to write binary data is

       int fwrite_matrix(file,m,nrl,nrl,ncl,nch,row_title,column_title)

 An example of using these routines is provided in the file `bf_test.c`, which
 generates binary files for the demo file `demo/binary.dem`.

 The `index` keyword is not supported, since the file format allows only one
 surface per file.  The `every` and `using` filters are supported.  `using`
 operates as if the data were read in the above triplet form.
^ <a href="http://www.gnuplot.vt.edu/gnuplot/gpdocs/binary.html">Binary File Splot Demo.</a>
4 example datafile
?commands splot datafile example
?splot datafile example
?splot example
 A simple example of plotting a 3-d data file is

       splot 'datafile.dat'

 where the file "datafile.dat" might contain:

       # The valley of the Gnu.
          0 0 10
          0 1 10
          0 2 10

          1 0 10
          1 1 5
          1 2 10

          2 0 10
          2 1 1
          2 2 10

          3 0 10
          3 1 0
          3 2 10

 Note that "datafile.dat" defines a 4 by 3 grid ( 4 rows of 3 points each ).
 Rows (datablocks) are separated by blank records.

^ <img align=bottom src="http://www.nas.nasa.gov/~woo/gnuplot/doc/splot.gif" alt="[splot.gif]" width=640 height=480>
 Note also that the x value is held constant within each dataline.  If you
 instead keep y constant, and plot with hidden-line removal enabled, you will
 find that the surface is drawn 'inside-out'.

 Actually for grid data it is not necessary to keep the x values constant
 within a datablock, nor is it necessary to keep the same sequence of y
 values.  `gnuplot` requires only that the number of points be the same for
 each datablock.  However since the surface mesh, from which contours are
 derived, connects sequentially corresponding points, the effect of an
 irregular grid on a surface plot is unpredictable and should be examined
 on a case-by-case basis.
4 matrix
?commands splot datafile matrix
?splot datafile matrix
?splot matrix
?data-file matrix
?datafile matrix
?matrix
 The `matrix` flag indicates that the ASCII data are stored in matrix format.
 The z-values are read in a row at a time, i. e.,
       z11 z12 z13 z14 ...
       z21 z22 z23 z24 ...
       z31 z32 z33 z34 ...
 and so forth.  The row and column indices are used for the x- and y-values.
3 grid_data
?commands splot grid_data
?splot grid_data
?grid_data
 The 3D routines are designed for points in a grid format, with one sample,
 datapoint, at each mesh intersection; the datapoints may originate from
 either evaluating a function, see `set isosamples`, or reading a datafile,
 see `splot datafile`.  The term "isoline" is applied to the mesh lines for
 both functions and data.  Note that the mesh need not be rectangular in x
 and y, as it may be parameterized in u and v, see `set isosamples`.

 However, `gnuplot` does not require that format.  In the case of functions,
 'samples' need not be equal to 'isosamples', i.e., not every x-isoline
 sample need intersect a y-isoline. In the case of data files, if there
 are an equal number of scattered data points in each datablock, then
 "isolines" will connect the points in a datablock, and "cross-isolines"
 will connect the corresponding points in each datablock to generate a
 "surface".  In either case, contour and hidden3d modes may give different
 plots than if the points were in the intended format.  Scattered data can be
 converted to a {different} grid format with `set dgrid3d`.

 The contour code tests for z intensity along a line between a point on a
 y-isoline and the corresponding point in the next y-isoline.  Thus a `splot`
 contour of a surface with samples on the x-isolines that do not coincide with
 a y-isoline intersection will ignore such samples. Try:
        set xrange [-pi/2:pi/2]; set yrange [-pi/2:pi/2]
        set function style lp
        set contour
        set isosamples 10,10; set samples 10,10;
        splot cos(x)*cos(y)
        set samples 4,10; replot
        set samples 10,4; replot

3 splot_overview
?commands splot_overview
? splot_overview
 `splot` can display a surface as a collection of points, or by connecting
 those points.  As with `plot`, the points may be read from a data file or
 result from evaluation of a function at specified intervals, see `set
 isosamples`.  The surface may be approximated by connecting the points
 with straight line segments, see `set surface`, in which case the surface
 can be made opaque with `set hidden3d.`  The orientation from which the 3d
 surface is viewed can be changed with `set view`.

 Additionally, for points in a grid format, `splot` can interpolate points
 having a common amplitude (see `set contour`) and can then connect those
 new points to display contour lines, either directly with straight-line
 segments or smoothed lines (see `set cntrparams`).  Functions are already
 evaluated in a grid format, determined by `set isosamples` and `set samples`,
 while file data must either be in a grid format, as described in `data-file`,
 or be used to generate a grid (see `set dgrid3d`).

 Contour lines may be displayed either on the surface or projected onto the
 base.  The base projections of the contour lines may be written to a
 file, and then read with `plot`, to take advantage of `plot`'s additional
 formatting capabilities.
2 test
?commands test
?test
 `test` creates a display of line and point styles and other useful things
 appropriate for the terminal you are using.

 Syntax:
       test
2 update
?commands update
?update
 This command writes the current values of the fit parameters into the given
 file, formatted as an initial-value file (as described in the `fit`section).
 This is useful for saving the current values for later use or for restarting
 a converged or stopped fit.

 Syntax:
       update <filename> {<filename>}

 If a second filename is supplied, the updated values are written to this
 file, and the original parameter file is left unmodified.

 Otherwise, if the file already exists, `gnuplot` first renames it by
 appending `.old` and then opens a new file.  That is, "`update 'fred'`"
 behaves the same as "`!rename fred fred.old; update 'fred.old' 'fred'`".
 [On DOS and other systems that use the twelve-character "filename.ext"
 naming convention, "ext" will be "`old`" and "filename" will be related
 (hopefully recognizably) to the initial name.  Renaming is not done at all
 on VMS systems, since they use file-versioning.]

 Please see `fit` for more information.
1 Graphical User Interfaces
?graphical user interfaces
?gui's
 Several graphical user interfaces have been written for `gnuplot` and one for
 win32 is included in this distribution.  In addition, there is a Macintosh
 interface at
^<a href="ftp://ftp.ee.gatech.edu/pub/mac/gnuplot">
        ftp://ftp.ee.gatech.edu/pub/mac/gnuplot
^</a>
 and several X11 interfaces include three Tcl/Tk located at the usual Tcl/Tk
 repositories.
1 Bugs
?bugs
 Floating point exceptions (floating point number too large/small, divide by
 zero, etc.) may occasionally be generated by user defined functions.  Some of
 the demos in particular may cause numbers to exceed the floating point range.
 Whether the system ignores such exceptions (in which case `gnuplot` labels
 the corresponding point as undefined) or aborts `gnuplot` depends on the
 compiler/runtime environment.

 The bessel functions do not work for complex arguments.

 The gamma function does not work for complex arguments.

 As of `gnuplot` version 3.7, all development has been done using ANSI C.
 With current operating system, compiler, and library releases, the OS
 specific bugs documented in release 3.5, now relegated to `old_bugs`, may
 no longer be relevant.

 Bugs reported since the current release may be located via the official
 distribution site:
        ftp://ftp.dartmouth.edu/pub/gnuplot
       http://www.cs.dartmouth.edu/gnuplot_info.html

 Please e-mail any bugs to [e-mail].
2 Old_bugs
?old_bugs
?os_bugs
 There is a bug in the stdio library for old Sun operating systems (SunOS
 Sys4-3.2).  The "%g" format for 'printf' sometimes incorrectly prints numbers
 (e.g., 200000.0 as "2").  Thus, tic mark labels may be incorrect on a Sun4
 version of `gnuplot`.  A work-around is to rescale the data or use the `set
 format` command to change the tic mark format to "%7.0f" or some other
 appropriate format.  This appears to have been fixed in SunOS 4.0.

 Another bug: On a Sun3 under SunOS 4.0, and on Sun4's under Sys4-3.2 and
 SunOS 4.0, the 'sscanf' routine incorrectly parses "00 12" with the format
 "%f %f" and reads 0 and 0 instead of 0 and 12.  This affects data input.  If
 the data file contains x coordinates that are zero but are specified like
 '00', '000', etc, then you will read the wrong y values.  Check any data
 files or upgrade the SunOS.  It appears to have been fixed in SunOS 4.1.1.

 Suns appear to overflow when calculating exp(-x) for large x, so `gnuplot`
 gets an undefined result.  One work-around is to make a user-defined function
 like e(x) = x<-500 ? 0 : exp(x).  This affects plots of Gaussians (exp(-x*x))
 in particular, since x*x grows quite rapidly.

 Microsoft C 5.1 has a nasty bug associated with the %g format for 'printf'.
 When any of the formats "%.2g", "%.1g", "%.0g", "%.g" are used, 'printf' will
 incorrectly print numbers in the range 1e-4 to 1e-1.  Numbers that should be
 printed in the %e format are incorrectly printed in the %f format, with the
 wrong number of zeros after the decimal point.  To work around this problem,
 use the %e or %f formats explicitly.

 `gnuplot`, when compiled with Microsoft C, did not work correctly on two VGA
 displays that were tested.  The CGA, EGA and VGA drivers should probably be
 rewritten to use the Microsoft C graphics library.  `gnuplot` compiled with
 Borland C++ uses the Turbo C graphics drivers and does work correctly with
 VGA displays.

 VAX/VMS 4.7 C compiler release 2.4 also has a poorly implemented %g format
 for 'printf'.  The numbers are printed numerically correct, but may not be in
 the requested format.  The K&R second edition says that for the %g format, %e
 is used if the exponent is less than -4 or greater than or equal to the
 precision.  The VAX uses %e format if the exponent is less than -1.  The VAX
 appears to take no notice of the precision when deciding whether to use %e or
 %f for numbers less than 1.  To work around this problem, use the %e or %f
 formats explicitly.  From the VAX C 2.4 release notes: e,E,f,F,g,G  Result
 will always contain a decimal  point.  For g and G, trailing zeros will not
 be removed from the result.

 VAX/VMS 5.2 C compiler release 3.0 has a slightly better implemented %g
 format than release 2.4, but not much.  Trailing decimal points are now
 removed, but trailing zeros are still not removed from %g numbers in
 exponential format.

 The two preceding problems are actually in the libraries rather than in the
 compilers.  Thus the problems will occur whether `gnuplot` is built using
 either the DEC compiler or some other one (e.g. the latest gcc).

 ULTRIX X11R3 has a bug that causes the X11 driver to display "every other"
 graph.  The bug seems to be fixed in DEC's release of X11R4 so newer releases
 of ULTRIX don't seem to have the problem.  Solutions for older sites include
 upgrading the X11 libraries (from DEC or direct from MIT) or defining
 ULTRIX_KLUDGE when compiling the x11.trm file.  Note that the kludge is not
 an ideal fix, however.

 The constant HUGE was incorrectly defined in the NeXT OS 2.0 operating
 system.  HUGE should be set to 1e38 in plot.h. This error has been corrected
 in the 2.1 version of NeXT OS.

 Some older models of HP plotters do not have a page eject command 'PG'.  The
 current HPGL driver uses this command in HPGL_reset.  This may need to be
 removed for these plotters.  The current PCL5 driver uses HPGL/2 for text as
 well as graphics.  This should be modified to use scalable PCL fonts.

 On the Atari version, it is not possible to send output directly to the
 printer (using `/dev/lp` as output file), since CRs are added to LFs in
 binary output.  As a work-around, write the output to a file and copy it to
 the printer afterwards using a shell command.

 On AIX 4, the literal 'NaNq' in a datafile causes the special internal value
 'not-a-number' to be stored, rather than setting an internal 'undefined'
 flag.  A workaround is to use `set missing 'NaNq'`.

 There may be an up-to-date list of bugs since the release on the WWW page:
       http://www.cs.dartmouth.edu/gnuplot_info.html

 Please report any bugs to [e-mail].