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Archive-name: graphics/gnuplot-faq Version: $Header: gnuplot-faq.html,v 1.11 94/04/05 00:45:18 ig25 Exp $ Posting-frequency: every 14 days X-Url: http://fg20.rz.uni-karlsruhe.de/~ig25/gnuplot-faq.html comp.graphics.gnuplot COMP.GRAPHICS.GNUPLOT FAQ (FREQUENT ANSWERED QUESTIONS) This is the FAQ (Frequently Answered Questions) list of the comp.graphics.gnuplot newsgroup, which discusses the gnuplot program for plotting 2D - and 3D - graphs. Most of the information in this document came from public discussion on comp.graphics.gnuplot; quotations are believed to be in the public domain. Here's a list of the questions. If you are looking for the answer for a specific question, look for the string Qx.x: at the beginning of a line, with x.x being the question number. Sections in this FAQ are * 0. Meta - Questions * 1. General Information * 2. Setting it up * 3. Working with it * 4. Wanted features * 5. Miscellaneous * 6. Making life easier * 7. Known problems * 8. Credits _________________________________________________________________ Questions: SECTION 0: META - QUESTIONS * Q0.1: Where do I get this document? * Q0.2: Where do I send comments about this document? SECTION 1: GENERAL INFORMATION * Q1.1: What is gnuplot? * Q1.2: How did it come about and why is it called gnuplot? * Q1.3: Does gnuplot have anything to do with the FSF and the GNU project? * Q1.4: What does gnuplot offer? * Q1.5: Is gnuplot suitable for batch processing? * Q1.6: Can I run gnuplot on my computer? SECTION 2: SETTING IT UP * Q2.1: What is the current version of gnuplot? * Q2.2: Where can I get gnuplot? * Q2.3: How do I get gnuplot to compile on my system? * Q2.4: What documentation is there, and how do I get it? SECTION 3: WORKING WITH IT * Q3.1: How do I get help? * Q3.2: How do I print out my graphs? * Q3.3: How do I include my graphs in <word processor>? SECTION 4: WANTED FEATURES * Q4.1: Does gnuplot have hidden line removal? * Q4.2: Does gnuplot support bar-charts/histograms/boxes? * Q4.3: Does gnuplot support multiple y-axes on a single plot? * Q4.4: Can I put multiple plots on a single page? * Q4.5: Can I put both data files and commands into a single file? * Q4.6: Can I put Greek letters and super/subscripts into my labels? * Q4.7 Can I do 1:1 scaling of axes? * Q4.8: Can I put tic marks for x and y axes into 3d plots? * Q4.9: Does gnuplot support a driver for ? * Q4.10: Can I put different text sizes into my plots? SECTION 5: MISCELLANEOUS * Q5.1: I've found a bug, what do I do? * Q5.2: Can I use gnuplot routines for my own programs? * Q5.3: What extensions have people made to gnuplot? Where can I get them? * Q5.4: Can I do heavy - duty data processing with gnuplot? * Q5.5: I have ported gnuplot to another system, or patched it. What do I do? SECTION 6: MAKING LIFE EASIER * Q6.1: How do I plot two functions in non - overlapping regions? * Q6.2: How do I run my data through a filter before plotting? * Q6.3: How do I make it easier to use gnuplot with LaTeX? * Q6.4: How do I save and restore my settings? * Q6.5: How do I plot lines (not grids) using splot? * Q6.6: How do I plot a function f(x,y) which is bounded by other functions in the x-y plain? * Q6.7: How do I get rid of <feature in a plot>? SECTION 7: KNOWN PROBLEMS * Q7.1: Gnuplot is not plotting any points under X11! How come? * Q7.2: My isoline data generated by a Fortran program is not handled correctly. What can I do? * Q7.3: Why does gnuplot ignore my very small numbers? * Q7.4: Gnuplot is plotting nothing when run via gnuplot <filename>! What can I do? * Q7.5: My formulas are giving me nonsense results! What's going on? SECTION 8: CREDITS _________________________________________________________________ Questions and Answers: SECTION 0: META - QUESTIONS. Q0.1: Where do I get this document? This document is posted about once every two weeks to the newsgroups comp.graphics.gnuplot, comp.answers and news.answers. Like many other FAQ's, its newest (plaintext) version is available via anonymous ftp from ftp://rtfm.mit.edu/pub/usenet/news.answers/graphics/gnuplot-faq . If you have access to the WWW, you can get the newest version of this document from http://fg20.rz.uni-karlsruhe.de/~ig25/gnuplot-faq.html Q0.2: Where do I send comments about this document? Send comments, suggestions etc. via e-mail to Thomas Koenig , ig25@rz.uni-karlsruhe.de or ig25@dkauni2.bitnet. _________________________________________________________________ SECTION 1: GENERAL INFORMATION Q1.1: What is gnuplot? Gnuplot is a command-driven interactive function plotting program. It can be used to plot functions and data points in both two- and three- dimensional plots in many different formats, and will accommodate many of the needs of today's scientists for graphic data representation. Gnuplot is copyrighted, but freely distributable; you don't have to pay for it. Q1.2: How did it come about and why is it called gnuplot? The authors of gnuplot are: Thomas Williams, Colin Kelley, Russell Lang, Dave Kotz, John Campbell, Gershon Elber, Alexander Woo and many others. The following quote comes from Thomas Williams: I was taking a differential equation class and Colin was taking Electromagnetics, we both thought it'd be helpful to visualize the mathematics behind them. We were both working as sys admin for an EE VLSI lab, so we had the graphics terminals and the time to do some coding. The posting was better received than we expected, and prompted us to add some, albeit lame, support for file data. Any reference to GNUplot is incorrect. The real name of the program is "gnuplot". You see people use "Gnuplot" quite a bit because many of us have an aversion to starting a sentence with a lower case letter, even in the case of proper nouns and titles. Gnuplot is not related to the GNU project or the FSF in any but the most peripheral sense. Our software was designed completely independently and the name "gnuplot" was actually a compromise. I wanted to call it "llamaplot" and Colin wanted to call it "nplot." We agreed that "newplot" was acceptable but, we then discovered that there was an absolutely ghastly pascal program of that name that the Computer Science Dept. occasionally used. I decided that "gnuplot" would make a nice pun and after a fashion Colin agreed. Q1.3: Does gnuplot have anything to do with the FSF and the GNU project? Gnuplot is neither written nor maintained by the FSF. It is not covered by the General Public License, either. However, the FSF has decided to distribute gnuplot as part of the GNU system, because it is useful, redistributable software. Q1.4: What does gnuplot offer? + Plotting of two - dimensional functions and data points in many different styles (points, lines, error bars) + plotting of three - dimensional data points and surfaces in many different styles (contour plot, mesh). + support for complex arithmetic + self - defined functions + support for a large number of operating systems, graphics file formats and devices + extensive on-line help + labels for title, axes, data points + command line editing and history on most platforms Q1.5: Is gnuplot suitable for batch processing? Yes. You can read in files from the command line, or you can redirect your standard input to read from a file. Both data and command files can be generated automatically, from data acquisition programs or whatever else you use. Q1.6: Can I run gnuplot on my computer? Gnuplot is available for a number of platforms. These are: Unix (X11 and NeXTSTEP), VAX/VMS, OS/2, MS-DOS, Amiga, MS-Windows, OS-9/68k, Atari ST and the Macintosh. Modifications for NEC PC-9801 are said to exist (where?). _________________________________________________________________ SECTION 2: SETTING IT UP Q2.1: What is the current version of gnuplot? The current version of gnuplot is 3.5, which is a bugfix release over 3.4. Q2.2: Where can I get gnuplot? [This information may be dated, due to the release of gnuplot 3.5. Please report any inaccuracies, if you find them. Ed.] All of the later addresses refer to ftp sites. Please note that it is preferable for you to use the symbolic name, rather than the IP address given in brackets, because that address is much more subject to change. The official distribution site for the gnuplot source is ftp.dartmouth.edu [129.170.16.4], the file is called /pub/gnuplot/gnuplot.3.5.tar.Z. Official mirrors of that distribution are (for Australia) monu1.cc.monash.edu.au [130.194.1.101] and (for Europe) irisa.irisa.fr [131.254.254.2]. You can also get it from your friendly neighbourhood comp.sources.misc archive. MS-DOS and MS-Windows binaries are available from + oak.oakland.edu (North America) [141.210.10.117] as pub/msdos/plot/gpt35*.zip, + garbo.uwasa.fi (Europe) [128.214.87.1] as /pc/plot/gpt35*.zip and + archie.au (Australia) [139.130.4.6] as micros/pc/oak/plot/gpt35*.zip. The files are: gpt35doc.zip, gpt35exe.zip, gpt35src.zip and gpt35win.zip. There is a special MS-DOS version for 386 or better processors; it is available from the official gnuplot sites as DOS34.zip. OS/2 2.x binaries are at ftp-os2.nmsu.edu [128.123.35.151], in /os2/2.x/unix/gnuplt35.zip . Amiga sources and binaries are available from ftp.wustl.edu [128.252.135.4] as /pub/aminet/util/gnu/gnuplot-3.5.lha; there are numerous mirrors of this distribution, for example ftp.uni-kl.de, oes.orst.edu or ftp.luth.se. The NeXTSTEP front end can be found at sonata.cc.purdue.edu and cs.orst.edu. A version for OS-9/68K can be found at cabrales.cs.wisc.edu [128.105.36.20] as /pub/OSK/GRAPHICS/gnuplot32x.tar.Z; it includes both X-Windows and non - X-windows versions. A version of gnuplot for the Mac can reportedly be found on archive.umich.edu and sumex-aim.stanford.edu, directories unknown. People without ftp access can use an ftp-mail server; send a message saying 'help' to bitftp@pucc.bitnet (for BITNET only) or to ftpmail@ftp.dartmouth.edu. For a uuencoded copy of the the gnuplot sources (compressed tar file), send this as the body of a message to ftpmail@ftp.dartmouth.edu: open cd pub/gnuplot mode binary get gnuplot3.5.tar.Z quit If you have some problem, you might need to stick reply-to <your-email-address-here> before all the above. It is a good idea to look for a nearby ftp site when downloading things. You can use archie for this. See if an archie client is installed at your system (by simply typing archie at the command prompt), or send mail to archie@sura.net with the word 'help' in both the subject line and the body of the mail. However, be aware that the version you find at a near ftp site may well be out of date; check the last modification date and the number of bytes against the newest release at one of the official servers. Q2.3: How do I get gnuplot to compile on my system? As you would any other installation. Read the files README and README.Install, edit the Makefile according to taste, and run make or whatever is suitable for your operating system. If you get a complaint about a missing file libplot.a or something similar when building gnuplot for X11, remove -DUNIXPLOT from the TERMFLAGS= line, remove -lplot from the DTBS= line and run again. If you are making X11 on a sun, type 'make x11_sun'. Q2.4: What documentation is there, and how do I get it? The documentation is included in the source distribution. Look at the docs subdirectory, where you'll find + a Unix man page, which says how to start gnuplot + a help file, which also can be printed as a manual + a tutorial on using gnuplot with LaTeX + a quick reference summary sheet for TeX only PostScript copies of the documentation can be ftp'd from ftp.dartmouth.edu, in pub/gnuplot, as manual.ps.Z and tutorial.ps.Z A Chinese translation of the manual can be found on ftp://servers.nctu.edu.tw/misc/environment/NCTU_EV/classnote/gn uplot.ps.gz . _________________________________________________________________ SECTION 3: WORKING WITH IT Q3.1: How do I get help? Give the 'help' command at the initial prompt. After that, keep looking through the keywords. Good starting points are 'plot' and 'set'. Read the manual, if you have it. Look through the demo subdirectory; it should give you some ideas. Ask your colleagues, the system administrator or the person who set up gnuplot. Post a question to comp.graphics.gnuplot or send mail to the gatewayed mailing list info-gnuplot@dartmouth.edu. If you want to subscribe to the mailing list, send mail to info-gnuplot-request@dartmouth.edu, but please don't do this if you can get comp.graphics.gnuplot directly. If you pose a question there, it is considered good form to solicit e-mail replies and post a summary. Q3.2: How do I print out my graphs? The kind of output produced is determined by the 'set terminal' command; for example, 'set terminal postscript' will produce the graph in PostScript format. Output can be redirected using the 'set output' command. As an example, the following prints out a graph of sin(x) on a Unix machine running X - Windows. gnuplot> plot [-6:6] sin(x) gnuplot> set terminal postscript Terminal type set to 'postscript' Options are 'landscape monochrome "Courier" 14' gnuplot> set output "sin.ps" gnuplot> replot gnuplot> set output # set output back to default gnuplot> set terminal x11 # ditto for terminal type gnuplot> ! lp -ops sin.ps # print ps - File (site dependent) request id is lprint-3433 (standard input) lp: printed file sin.ps on fg20.rz.uni-karlsruhe.de (5068 Byte) ! gnuplot> Q3.3: How do I include my graphs in <word processor>? Basically, you save your plot to a file in a format your word processor can understand (using "set term" and "set output", see above), and then you read in the plot from your word processor. Details depend on the kind of word processor you use; use "set term" to get a list of available file formats. Many word processors can use Encapsulated PostScript for graphs. This can be generated by the "set terminal postscript eps" command. Most MS-DOS word processors understand HPGL (terminal type hpgl). With TeX, it depends on what you use to print your dvi files. If you use dvips or dvi2ps, you can use Encapsulated PostScript. For emTeX (popular for MS-DOS), you can use emTeX, otherwise use the LaTeX terminal type, which generates a picture environment. If nothing else helps, try using the pgm or ppm format and converting it to a bitmap format your favourite word processor can understand. An invaluable tool for this is Jef Poskanzer's PBMPLUS package. The PBMPLUS package is available in the contrib distribution for Xwindows. The original site for this is ftp.x.org:/contrib, there are many mirrors, e.g. ftp.th-darmstadt.de:/pub/X11/contrib or sunsite.unc.edu:/pub/X11/contrib. The most recent release of pbm by the author is dated December 91 and is called pbmplus10dec91.tar.Z There is new version including lots of patches from the net that is not maintained by the author called netpbm, with the newest version called netpbm-7dec1993.tar.gz. Check archie (see Q2.2 ) for an archive site near you. _________________________________________________________________ SECTION 4: WANTED FEATURES Q4.1: Does gnuplot have hidden line removal? Version 3.5 supports hidden line removal on all platforms except MS-DOS; use the command set hidden3d If someone can solve the 64K DGROUP memory problem, gnuplot would support hidden line removal on MS-DOS as well. Version 3.2 supports limited hidden line removal. Q4.2: Does gnuplot support bar-charts/histograms/boxes? As of version 3.4, it does. Q4.3: Does gnuplot support multiple y-axes on a single plot? Yes, with two unofficial mods, multiplot.shar and borders.shar. Send mail to woo@playfair.stanford.edu. Q4.4: Can I put multiple plots on a single page? Yes, with the multiplot.shar mod. If you are using PostScript output, check out mpage, which can be ftp'd from ftp.eng.umd.edu:pub/misc/mpage-2.tar.Z Q4.5: Can I put both data files and commands into a single file? This is a feature which will probably be in gnuplot 3.6, which is in early development. Ask for the mixed.shar patch from woo@playfair.stanford.edu. Q4.6: Can I put Greek letters and super/subscripts into my labels? You might try using the LaTeX terminal type and putting text like \alpha_{3} into it. If you use PostScript output, you might find something in the Green subdirectory of the gpcontrb file (see Q5.3). David Denholm has written a PostScript terminal which allows for super/and subscripts, such as a^x or { Symbol a }. Ftp to sotona.phys.soton.ac.uk[152.78.192.42] and get divpost34.trm. To install it, copy it over ~gnuplot/term/post.trm and recompile. A never version is mattpost.trm, rewritten by Matt Heffron. Q4.7: Can I do 1:1 scaling of axes? Not easily. Q4.8: Can I put tic marks for x and y axes into 3d plots? In version 3.5, you can. Q4.9: Does gnuplot support a driver for ? To see a list of the available graphic drivers for your installation of gnuplot, type "set term". Some graphics drivers are included in the normal distribution, but are uncommented by default. If you want to use them, you'll have to change ~gnuplot/term.h. Q4.10: Can I put different text sizes into my plots? If you use PostScript output, you can use Dave Denholm's and Matt Heffron's updated PostScript driver, /sotona.phys.soton.ac.uk:/mattpost.trm (see also Q4.6 ). _________________________________________________________________ SECTION 5: MISCELLANEOUS Q5.1: I've found a bug, what do I do? First, try to see whether it actually is a bug, or whether it is a feature which may be turned off by some obscure set - command. Next, see wether you have an old version of gnuplot; if you do, chances are the bug has been fixed in a newer release. If, after checking these things, you still are convinced that there is a bug, proceed as follows. If you have a fairly general sort of bug report, posting to comp.graphics.gnuplot is probably the way to go. If you have investigated a problem in detail, especially if you have a context diff that fixes the problem, please e-email a report to bug-gnuplot@dartmouth.edu. The bug-gnuplot list is for reporting and collecting bug fixes, the comp.graphics.gnuplot newsgroup will be more help for finding work arounds or actually solving gnuplot related problems. If you do send in a bug report, be sure and include the version of gnuplot (including patchlevel), terminal driver, operating system, an exact description of the bug and input which can reproduce the bug. Also, any context diffs should be referenced against the latest official version of gnuplot if at all possible. Q5.2: Can I use gnuplot routines for my own programs? Yes. John Campbell has written gplotlib, a version of gnuplot as C subroutines callable from a C program. This is available as gplotlib.tar.Z on the machine ftp.nau.edu in the directory /pub/gplotlib.tar.Z. This library has been updated to be compatible with version 3.5. Ask woo@playfair.stanford.edu. Q5.3: What extensions have people made to gnuplot? Where can I get them? [A new gpcontrb is under construction. A. Woo] Extensions have been put into the file gpcontrb.tar.Z, which is available with the 3.5 release, from the same places you can download the main distribution from. Note that it has a size of 3.5 megabytes. It contains the following subdirectories: bigler subdirectory: From: bigler@cicg-calcul.grenet.fr Subject: Multiple plots from a Fortran program budelsky subdirectory: From: budelsky@haegar.ikp.uni-koeln.de Subject: This is the information file for porting gnuplot 3.2 to OS-9/68000 byrne subdirectory: From: "Margaret R. Byrne" Subject: congp3d3 preprocessor to draw contour plots on irregular regions. clark subdirectory: From: Michael Clark Subject: data filtering: adds point_skip & point_offs clift subdirectory: From: ssclift@neumann.uwaterloo.ca (Simon Clift) Subject: Re: Running gnuplot from Fortran, (and C) green subdirectory: From: Roque Donizete de Oliveira Subject: PostScript Greek symbols in gnuplot, new prologue hanna subdirectory: From: gregor@kafka.saic.com (gregg hanna) Subject: x11-library mode, gnulib_x11.[c,h], xlibtest.c,makefile.xlib klosowski subdirectory: From: Carsten Steger Subject: New file "klein.dat" From: przemek@rrdstrad.nist.gov (Przemek Klosowski) Subject: calling gnuplot from Fortran kocaturk subdirectory: From: mustafa@seas.smu.edu (Mustafa Kocaturk) Subject: Histograms in gnuplot richardson subdirectory: From: amr@chiton.ucsd.edu (Tony Richardson) Subject: Programmatic control of gnuplot from Unix rosendorf subdirectory: From: prf@jprix.che.wisc.edu Subject: Multiple plots on a page vanzandt subdirectory: From: James R. Van Zandt Subject: Spline generating program white subdirectory: From: gwhite@bionet.bio.dfo.ca Subject: gnuplot 3.2 for Titan 3000 woo subdirectory: From: "Alex Woo" Subject: two additional title lines and fixes to errorbar style yamamoto subdirectory: From: "NOBORU YAMAMOTO " Subject: Re: gnuplot on Apple Macintosh, "diff -c" of version 3.0 (now includes binaries) castro subdirectory: From: maurice@bruce.cs.monash.edu.au (Maurice Castro) Subject: Controlling gnuplot from another Windows program grammes subdirectory: From: ph12hucg@rz.uni-sb.de (Carsten Grammes) Subject: Nonlinear least squares fit mechanism henke subdirectory: From: mgr@asgard.bo.open.de (Lars Hanke) Subject: Re: Changes to gnuplot 3.3b9 walton subdirectory: From: dwalton@athena.mit.edu (Dave Walton) Subject: Inter Process Communication stuff Q5.4: Can I do heavy - duty data processing with gnuplot? Gnuplot alone is not suited very well for this. One thing you might try is fudgit, an interactive multi-purpose fitting program written by Martin-D. Lacasse (isaac@frodo.physics.mcgill.ca). It can use gnuplot as its graphics back end and is available from ftp.physics.mcgill.ca in /pub/Fudgit/fudgit_2.33.tar.Z [132.206.9.13], and from the main Linux server, tsx-11.mit.edu [18.172.1.2] and its numerous mirrors around the world as /pub/linux/sources/usr.bin/fudgit-2.33.tar.z. Versions are available for AIX, Data General, HP-UX, IRIX 4, Linux, NeXT, Sun3, Sun4, Ultrix, OS/2 and MS-DOS. The MS-DOS version is available on simtel20 mirrors (simtel20 itself has closed down) in the "math" subdirectory as fudg_231.zip. Carsten Grammes has written a fitting program which goes together with gnuplot; it is called gnufit and is available from the official gnuplot sites, as the files gnufit12.info, gnufit12.tar.gz (source) and gft12dos.zip (MS-DOS). Michael Courtney has written a program called lsqrft, which uses the Levenberg - Marquardt - Algorithm for fitting data to a function. It is avialiable from ftp.cdrom.com as /pub/os2/2_x/unix/lsqrft13.zip; sources, which should compile on Unix, and executables for MS-DOS and OS/2 2.x are included. There is an interface to the OS/2 presentation manager. You might also want to look at the applications developed by the Software Tools Group (STG) at the National Center for Supercomputing Applications. Ftp to ftp.ncsa.uiuc.edu [141.142.20.50] and get the file README.BROCHURE for more information. Q5.5: I have ported gnuplot to another system, or patched it. What do I do? If your patch is small, mail it to bug-gnuplot@dartmouth.edu, with a thorough description of what the patch is supposed to do, which version of gnuplot it is relative to, etc. Please don't mail it to the FAQ maintainer. If your modifications are extensive (such as a port to another system), upload your modifications to ftp.dartmouth.edu:/pub/dropoff. Please drop a note to David.Kotz@dartmouth.edu, the maintainer of the gnuplot subdirectory there, plus a note to bug-gnuplot@dartmouth.edu. _________________________________________________________________ SECTION 6: MAKING LIFE EASIER Q6.1: How do I plot two functions in non - overlapping regions? Use a parametric plot. An example: set parametric a=1 b=3 c=2 d=4 x1(t) = a+(b-a)*t x2(t) = c+(d-c)*t f1(x) = sin(x) f2(x) = x**2/8 plot [t=0:1] x1(t),f1(x1(t)) title "f1", x2(t), f2(x2(t)) title "f2" Q6.2: How do I run my data through a filter before plotting? If your system supports the popen() - function, as Unix does, you should be able to run the output through another process such as a short awk program (use the "help plot datafile" command for an example). Unfortunately, in 3.2, there is a rather short limitation on the maximum argument length, so your command line may be truncated (usually, this will mean that awk cannot find the filename). Also, you may need to escape the $ - characters in your awk programs. As of version 3.4, gnuplot includes the thru - keyword for the plot command for running data files through a gnuplot - defined function. You can also get divhack.trm from sotona.phys.soton.ac.uk[152.78.192.42] via anonymous ftp. It allows expressions of the kind gnuplot> plot "datafile" using A:B:C where A,B,C,... are now either a column number, as usual, or an arbitrary expression enclosed in ()'s, and using $1,$2,etc to access the data columns. Q6.3: How do I make it easier to use gnuplot with LaTeX? There is a set of LaTeX macros and shell scripts that are meant to make your life easier when using gnuplot with LaTeX. This package can be found on ftp.dartmouth.edu [129.170.16.54] in pub/gnuplot/latex.shar, by David Kotz. For example, the program "plotskel" can turn a gnuplot-output file plot.tex into a skeleton file skel.tex, that has the same size as the original plot but contains no graph. With the right macros, the skeleton can be used for preliminary LaTeX passes, reserving the full graph for later passes, saving tremendous amounts of time. Q6.4: How do I save and restore my settings? Use the "save" and "load" commands for this; see "help save" and "help load" for details. Q6.5: How do I plot lines (not grids) using splot? If the data in a data file for splot is arranged in such a way that each one has the same number of data points (using blank lines as delimiters, as usual), splot will plot the data with a grid. If you want to plot just lines, use a different number of data entries (you can do this by doubling the last data point, for example). Don't forget to set parametric mode, of course. Q6.6: How do I plot a function f(x,y) which is bounded by other functions in the x-y plain? An example: f(x,y) = x**2 + y **2 x(u) = 3*u yu(x) = x**2 yl(x) = -x**2 set parametric set cont splot [0:1] [0:1] u,yl(x(u))+(yu(x(u)) - yl(x(u)))*v,\ f(x(u), (yu(x(u)) - yl(x(u)))*v) Q6.7: How do I get rid of <feature in a plot>? Usually, there is a set command to do this; do a gnuplot> ?set no for a short overview. _________________________________________________________________ SECTION 7: KNOWN PROBLEMS Q7.1: Gnuplot is not plotting any points under X11! How come? Very probably, you still are using an old version of gnuplot_x11. Remove that, then do a full installation. On VMS, you need to make several symbols: $ gnuplot_x11 :== $disk:[directory]gnuplot_x11 $ gnuplot :== $disk:[directory]gnuplot.exe $ def/job GNUPLOT$HELP disk:[directory]gnuplot.hlb Then run gnuplot from your command line, and use gnuplot> set term x11 Q7.2: My isoline data generated by a Fortran program is not handled correctly. What can I do? One known cause for this is the use of list - directed output (as in WRITE(10,*) for generating blank lines. Fortran uses ASA carriage control characters, and for list - directed output this results in a space being output before the newline. Gnuplot does not like this. The solution is to generate blank lines using formatted output, as in WRITE(10,'()'). If you use carriage return files in VMS Fortran, you may have to open the file with OPEN(...,CARRIAGECONTROL='DTST') or convert it using the DECUS utility ATTRIB.EXE: VMS> ATTRIB/RATTRIB=IMPDTED FOR010.DAT Q7.3: Why does gnuplot ignore my very small numbers? Gnuplot treats all numbers less than 1e-08 as zero, by default. Thus, if you are trying to plot a collection of very small numbers, they may be plotted as zero. Worse, if you're plotting on a log scale, they will be off scale. Or, if the whole set of numbers is "zero", your range may be considered empty: gnuplot> plot 'test1' Warning: empty y range [4.047e-19:3e-11], adjusting to [-1:1] gnuplot> set yrange [4e-19:3e-11] gnuplot> plot 'test1' ^ y range is less than `zero` The solution is to change gnuplot's idea of "zero": gnuplot> set zero 1e-20 For more information, gnuplot> help set zero Q7.4: Gnuplot is plotting nothing when run via gnuplot <filename>! What can I do? Put a pause -1 after the plot command in the file. Q7.5: My formulas are giving me nonsense results! What's going on? Gnuplot does integer, and not floating point, arithmetic on integer expressions. For example, the expression 1/3 evaluates to zero. If you want floating point expressions, supply trailing dots for your floating point numbers. Example: gnuplot> print 1/3 0 gnuplot> print 1./3. 0.333333 This way of evaluating integer expressions is shared by both C and Fortran. _________________________________________________________________ SECTION 8: CREDITS This list was initially compiled by John Fletcher with contributions from Russell Lang, John Campbell, David Kotz, Rob Cunningham, Daniel Lewart and Alex Woo. Reworked by Thomas Koenig from a draft by Alex Woo, with corrections and additions from Alex Woo, John Campbell, Russell Lang, David Kotz and many corrections from Daniel Lewart; Axel Eble and Jutta Zimmermann helped with the conversion to HTML. _________________________________________________________________ Thomas Koenig, ig25@rz.uni-karlsruhe.de, 1994-03-28 -- Thomas Koenig, ig25@rz.uni-karlsruhe.de, ig25@dkauni2.bitnet, The joy of engineering is to find a straight line on a double logarithmic diagram.