OS/2 Shareware BBS: 10 Tools

home *** CD-ROM | disk | FTP | other *** search

/ OS/2 Shareware BBS: 10 Tools / 10-Tools.zip / octa21fb.zip / octave / doc / octave.i05 (.txt) < prev next >

Wrap

GNU Info File | 2000-01-15 | 51KB | 974 lines

This is Info file octave, produced by Makeinfo-1.64 from the input file octave.tex. START-INFO-DIR-ENTRY * Octave: (octave). Interactive language for numerical computations. END-INFO-DIR-ENTRY Copyright (C) 1996, 1997 John W. Eaton. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions. File: octave, Node: Script Files, Next: Dynamically Linked Functions, Prev: Function Files, Up: Functions and Scripts Script Files ============ A script file is a file containing (almost) any sequence of Octave commands. It is read and evaluated just as if you had typed each command at the Octave prompt, and provides a convenient way to perform a sequence of commands that do not logically belong inside a function. Unlike a function file, a script file must *not* begin with the keyword `function'. If it does, Octave will assume that it is a function file, and that it defines a single function that should be evaluated as soon as it is defined. A script file also differs from a function file in that the variables named in a script file are not local variables, but are in the same scope as the other variables that are visible on the command line. Even though a script file may not begin with the `function' keyword, it is possible to define more than one function in a single script file and load (but not execute) all of them at once. To do this, the first token in the file (ignoring comments and other white space) must be something other than `function'. If you have no other statements to evaluate, you can use a statement that has no effect, like this: # Prevent Octave from thinking that this # is a function file: 1; # Define function one: function one () ... To have Octave read and compile these functions into an internal form, you need to make sure that the file is in Octave's `LOADPATH', then simply type the base name of the file that contains the commands. (Octave uses the same rules to search for script files as it does to search for function files.) If the first token in a file (ignoring comments) is `function', Octave will compile the function and try to execute it, printing a message warning about any non-whitespace characters that appear after the function definition. Note that Octave does not try to look up the definition of any identifier until it needs to evaluate it. This means that Octave will compile the following statements if they appear in a script file, or are typed at the command line, # not a function file: 1; function foo () do_something (); endfunction function do_something () do_something_else (); endfunction even though the function `do_something' is not defined before it is referenced in the function `foo'. This is not an error because Octave does not need to resolve all symbols that are referenced by a function until the function is actually evaluated. Since Octave doesn't look for definitions until they are needed, the following code will always print `bar = 3' whether it is typed directly on the command line, read from a script file, or is part of a function body, even if there is a function or script file called `bar.m' in Octave's `LOADPATH'. eval ("bar = 3"); bar Code like this appearing within a function body could fool Octave if definitions were resolved as the function was being compiled. It would be virtually impossible to make Octave clever enough to evaluate this code in a consistent fashion. The parser would have to be able to perform the call to `eval' at compile time, and that would be impossible unless all the references in the string to be evaluated could also be resolved, and requiring that would be too restrictive (the string might come from user input, or depend on things that are not known until the function is evaluated). Although Octave normally executes commands from script files that have the name `FILE.m', you can use the function `source' to execute commands from any file. - Built-in Function: source (FILE) Parse and execute the contents of FILE. This is equivalent to executing commands from a script file, but without requiring the file to be named `FILE.m'. File: octave, Node: Dynamically Linked Functions, Next: Organization of Functions, Prev: Script Files, Up: Functions and Scripts Dynamically Linked Functions ============================ On some systems, Octave can dynamically load and execute functions written in C++. Octave can only directly call functions written in C++, but you can also load functions written in other languages by calling them from a simple wrapper function written in C++. Here is an example of how to write a C++ function that Octave can load, with commentary. The source for this function is included in the source distributions of Octave, in the file `examples/oregonator.cc'. It defines the same set of differential equations that are used in the example problem of *Note Ordinary Differential Equations::. By running that example and this one, we can compare the execution times to see what sort of increase in speed you can expect by using dynamically linked functions. The function defined in `oregonator.cc' contains just 8 statements, and is not much different than the code defined in the corresponding M-file (also distributed with Octave in the file `examples/oregonator.m'). Here is the complete text of `oregonator.cc': just #include <octave/oct.h> DEFUN_DLD (oregonator, args, , "The `oregonator'.") { ColumnVector dx (3); ColumnVector x = args(0).vector_value (); dx(0) = 77.27 * (x(1) - x(0)*x(1) + x(0) - 8.375e-06*pow (x(0), 2)); dx(1) = (x(2) - x(0)*x(1) - x(1)) / 77.27; dx(2) = 0.161*(x(0) - x(2)); return octave_value (dx); } The first line of the file, #include <octave/oct.h> includes declarations for all of Octave's internal functions that you will need. If you need other functions from the standard C++ or C libraries, you can include the necessary headers here. The next two lines DEFUN_DLD (oregonator, args, , "The `oregonator'.") declares the function. The macro `DEFUN_DLD' and the macros that it depends on are defined in the files `defun-dld.h', `defun.h', and `defun-int.h' (these files are included in the header file `octave/oct.h'). Note that the third parameter to `DEFUN_DLD' (`nargout') is not used, so it is omitted from the list of arguments to in order to avoid the warning from gcc about an unused function parameter. simply declares an object to store the right hand sides of the differential equation, and The statement ColumnVector x = args(0).vector_value (); extracts a column vector from the input arguments. The variable `args' is passed to functions defined with `DEFUN_DLD' as an `octave_value_list' object, which includes methods for getting the length of the list and extracting individual elements. In this example, we don't check for errors, but that is not difficult. All of the Octave's built-in functions do some form of checking on their arguments, so you can check the source code for those functions for examples of various strategies for verifying that the correct number and types of arguments have been supplied. The next statements ColumnVector dx (3); dx(0) = 77.27 * (x(1) - x(0)*x(1) + x(0) - 8.375e-06*pow (x(0), 2)); dx(1) = (x(2) - x(0)*x(1) - x(1)) / 77.27; dx(2) = 0.161*(x(0) - x(2)); define the right hand side of the differential equation. Finally, we can return `dx': return octave_value (dx); The actual return type is `octave_value_list', but it is only necessary to convert the return type to an `octave_value' because there is a default constructor that can automatically create an object of that type from an `octave_value' object, so we can just use that instead. To use this file, your version of Octave must support dynamic linking. To find out if it does, type the command `octave_config_info ("dld")' at the Octave prompt. Support for dynamic linking is included if this command returns 1. To compile the example file, type the command `mkoctfile oregonator.cc' at the shell prompt. The script `mkoctfile' should have been installed along with Octave. Running it will create a file called `oregonator.oct' that can be loaded by Octave. To test the `oregonator.oct' file, start Octave and type the command oregonator ([1, 2, 3], 0) at the Octave prompt. Octave should respond by printing ans = 77.269353 -0.012942 -0.322000 You can now use the `oregonator.oct' file just as you would the `oregonator.m' file to solve the set of differential equations. On a 133 MHz Pentium running Linux, Octave can solve the problem shown in *Note Ordinary Differential Equations:: in about 1.4 second using the dynamically linked function, compared to about 19 seconds using the M-file. Similar decreases in execution time can be expected for other functions, particularly those that rely on functions like `lsode' that require user-supplied functions. Just as for M-files, Octave will automatically reload dynamically linked functions when the files that define them are more recent than the last time that the function was loaded. Two variables are available to control how Octave behaves when dynamically linked functions are cleared or reloaded. - Built-in Variable: auto_unload_dot_oct_files If the value of `auto_unload_dot_oct_files' is nonzero, Octave will automatically unload any `.oct' files when there are no longer any functions in the symbol table that reference them. - Built-in Variable: warn_reload_forces_clear If several functions have been loaded from the same file, Octave must clear all the functions before any one of them can be reloaded. If `warn_reload_forces_clear', Octave will warn you when this happens, and print a list of the additional functions that it is forced to clear. Additional examples for writing dynamically linked functions are available in the files in the `src' directory of the Octave distribution. Currently, this includes the files balance.cc fft2.cc inv.cc qzval.cc chol.cc filter.cc log.cc schur.cc colloc.cc find.cc lsode.cc sort.cc dassl.cc fsolve.cc lu.cc svd.cc det.cc givens.cc minmax.cc syl.cc eig.cc hess.cc pinv.cc expm.cc ifft.cc qr.cc fft.cc ifft2.cc quad.cc These files use the macro `DEFUN_DLD_BUILTIN' instead of `DEFUN_DLD'. The difference between these two macros is just that `DEFUN_DLD_BUILTIN' can define a built-in function that is not dynamically loaded if the operating system does not support dynamic linking. To define your own dynamically linked functions you should use `DEFUN_DLD'. There is currently no detailed description of all the functions that you can call in a built-in function. For the time being, you will have to read the source code for Octave. File: octave, Node: Organization of Functions, Prev: Dynamically Linked Functions, Up: Functions and Scripts Organization of Functions Distributed with Octave ================================================= Many of Octave's standard functions are distributed as function files. They are loosely organized by topic, in subdirectories of `OCTAVE-HOME/lib/octave/VERSION/m', to make it easier to find them. The following is a list of all the function file subdirectories, and the types of functions you will find there. `audio' Functions for playing and recording sounds. `control' Functions for design and simulation of automatic control systems. `elfun' Elementary functions. `general' Miscellaneous matrix manipulations, like `flipud', `rot90', and `triu', as well as other basic functions, like `is_matrix', `nargchk', etc. `image' Image processing tools. These functions require the X Window System. Input-ouput functions. `linear-algebra' Functions for linear algebra. `miscellaneous' Functions that don't really belong anywhere else. `plot' A set of functions that implement the MATLAB-like plotting functions. `polynomial' Functions for manipulating polynomials. `set' Functions for creating and manipulating sets of unique values. `signal' Functions for signal processing applications. `specfun' Special functions. `special-matrix' Functions that create special matrix forms. `startup' Octave's system-wide startup file. `statistics' Statistical functions. `strings' Miscellaneous string-handling functions. `time' Functions related to time keeping. % DO NOT EDIT! Generated automatically by munge-texi. File: octave, Node: Error Handling, Next: Input and Output, Prev: Functions and Scripts, Up: Top Error Handling ************** Octave includes several functions for printing error and warning messages. When you write functions that need to take special action when they encounter abnormal conditions, you should print the error messages using the functions described in this chapter. - Built-in Function: error (TEMPLATE, ...) The `error' function formats the optional arguments under the control of the template string TEMPLATE using the same rules as the `printf' family of functions (*note Formatted Output::.). The resulting message is prefixed by the string `error: ' and printed on the `stderr' stream. Calling `error' also sets Octave's internal error state such that control will return to the top level without evaluating any more commands. This is useful for aborting from functions or scripts. If the error message does not end with a new line character, Octave will print a traceback of all the function calls leading to the error. For example, given the following function definitions: function f () g () end function g () h () end function h () nargin == 1 || error ("nargin != 1"); end calling the function `f' will result in a list of messages that can help you to quickly locate the exact location of the error: f () error: nargin != 1 error: evaluating index expression near line 1, column 30 error: evaluating binary operator `||' near line 1, column 27 error: called from `h' error: called from `g' error: called from `f' If the error message ends in a new line character, Octave will print the message but will not display any traceback messages as it returns control to the top level. For example, modifying the error message in the previous example to end in a new line causes Octave to only print a single message: function h () nargin == 1 || error ("nargin != 1\n"); end f () error: nargin != 1 - Built-in Variable: error_text This variable contains the text of error messages that would have been printed in the body of the most recent `unwind_protect' or `try' statement or the TRY part of the most recent call to the `eval' function. Outside of the `unwind_protect' and `try' statements or the `eval' function, or if no error has occurred within them, the value of `error_text' is guaranteed to be the empty string. Note that the message does not include the first `error: ' prefix, so that it may easily be passed to the `error' function without additional processing(1). *Note The try Statement:: and *Note The unwind_protect Statement::. - Built-in Variable: beep_on_error If the value of `beep_on_error' is nonzero, Octave will try to ring your terminal's bell before printing an error message. The default value is 0. - Built-in Function: warning (MSG) Print a warning message MSG prefixed by the string `warning: '. After printing the warning message, Octave will continue to execute commands. You should use this function should when you want to notify the user of an unusual condition, but only when it makes sense for your program to go on. - Built-in Function: usage (MSG) Print the message MSG, prefixed by the string `usage: ', and set Octave's internal error state such that control will return to the top level without evaluating any more commands. This is useful for aborting from functions. After `usage' is evaluated, Octave will print a traceback of all the function calls leading to the usage message. You should use this function for reporting problems errors that result from an improper call to a function, such as calling a function with an incorrect number of arguments, or with arguments of the wrong type. For example, most functions distributed with Octave begin with code like this if (nargin != 2) usage ("foo (a, b)"); endif to check for the proper number of arguments. The following pair of functions are of limited usefulness, and may be removed from future versions of Octave. - Function File: perror (NAME, NUM) Print the error message for function NAME corresponding to the error number NUM. This function is intended to be used to print useful error messages for those functions that return numeric error codes. - Function File: strerror (NAME, NUM) Return the text of an error message for function NAME corresponding to the error number NUM. This function is intended to be used to print useful error messages for those functions that return numeric error codes. % DO NOT EDIT! Generated automatically by munge-texi. ---------- Footnotes ---------- (1) Yes, it's a kluge, but it seems to be a reasonably useful one. File: octave, Node: Input and Output, Next: Plotting, Prev: Error Handling, Up: Top Input and Output **************** There are two distinct classes of input and output functions. The first set are modeled after the functions available in MATLAB. The second set are modeled after the standard I/O library used by the C programming language and offer more flexibility and control over the output. When running interactively, Octave normally sends any output intended for your terminal that is more than one screen long to a paging program, such as `less' or `more'. This avoids the problem of having a large volume of output stream by before you can read it. With `less' (and some versions of `more') you can also scan forward and backward, and search for specific items. Normally, no output is displayed by the pager until just before Octave is ready to print the top level prompt, or read from the standard input (for example, by using the `fscanf' or `scanf' functions). This means that there may be some delay before any output appears on your screen if you have asked Octave to perform a significant amount of work with a single command statement. The function `fflush' may be used to force output to be sent to the pager (or any other stream) immediately. You can select the program to run as the pager by setting the variable `PAGER', and you can turn paging off by setting the value of the variable `page_screen_output' to 0. - Command: more - Command: more ON - Command: more OFF Turn output pagination on or off. Without an argument, `more' toggles the current state. - Built-in Variable: PAGER The default value is normally `"less"', `"more"', or `"pg"', depending on what programs are installed on your system. *Note Installation::. When running interactively, Octave sends any output intended for your terminal that is more than one screen long to the program named by the value of the variable `PAGER'. - Built-in Variable: page_screen_output If the value of `page_screen_output' is nonzero, all output intended for the screen that is longer than one page is sent through a pager. This allows you to view one screenful at a time. Some pagers (such as `less'--see *Note Installation::) are also capable of moving backward on the output. The default value is 1. - Built-in Variable: page_output_immediately If the value of `page_output_immediately' is nonzero, Octave sends output to the pager as soon as it is available. Otherwise, Octave buffers its output and waits until just before the prompt is printed to flush it to the pager. The default value is 0. - Built-in Function: fflush (FID) Flush output to FID. This is useful for ensuring that all pending output makes it to the screen before some other event occurs. For example, it is always a good idea to flush the standard output stream before calling `input'. * Menu: * Basic Input and Output:: * C-Style I/O Functions:: File: octave, Node: Basic Input and Output, Next: C-Style I/O Functions, Prev: Input and Output, Up: Input and Output Basic Input and Output ====================== * Menu: * Terminal Output:: * Terminal Input:: * Simple File I/O:: File: octave, Node: Terminal Output, Next: Terminal Input, Prev: Basic Input and Output, Up: Basic Input and Output Terminal Output --------------- Since Octave normally prints the value of an expression as soon as it has been evaluated, the simplest of all I/O functions is a simple expression. For example, the following expression will display the value of pi pi -| pi = 3.1416 This works well as long as it is acceptable to have the name of the variable (or `ans') printed along with the value. To print the value of a variable without printing its name, use the function `disp'. The `format' command offers some control over the way Octave prints values with `disp' and through the normal echoing mechanism. - Built-in Variable: ans This variable holds the most recently computed result that was not explicitly assigned to a variable. For example, after the expression 3^2 + 4^2 is evaluated, the value of `ans' is 25. - Built-in Function: disp (X) Display the value of X. For example, disp ("The value of pi is:"), disp (pi) -| the value of pi is: -| 3.1416 Note that the output from `disp' always ends with a newline. - Command: format OPTIONS Control the format of the output produced by `disp' and Octave's normal echoing mechanism. Valid options are listed in the following table. `short' Octave will try to print numbers with at least 3 significant figures within a field that is a maximum of 8 characters wide. If Octave is unable to format a matrix so that columns line up on the decimal point and all the numbers fit within the maximum field width, it switches to an `e' format. `long' Octave will try to print numbers with at least 15 significant figures within a field that is a maximum of 24 characters wide. As will the `short' format, Octave will switch to an `e' format if it is unable to format a matrix so that columns line up on the decimal point and all the numbers fit within the maximum field width. `long e' `short e' The same as `format long' or `format short' but always display output with an `e' format. For example, with the `short e' format, pi is displayed as `3.14e+00'. `long E' `short E' The same as `format long e' or `format short e' but always display output with an uppercase `E' format. For example, with the `long E' format, pi is displayed as `3.14159265358979E+00'. `free' `none' Print output in free format, without trying to line up columns of matrices on the decimal point. This also causes complex numbers to be formatted like this `(0.604194, 0.607088)' instead of like this `0.60419 + 0.60709i'. `bank' Print in a fixed format with two places to the right of the decimal point. `+' Print a `+' symbol for nonzero matrix elements and a space for zero matrix elements. This format can be very useful for examining the structure of a large matrix. `hex' Print the hexadecimal representation numbers as they are stored in memory. For example, on a workstation which stores 8 byte real values in IEEE format with the least significant byte first, the value of `pi' when printed in `hex' format is `400921fb54442d18'. This format only works for numeric values. `bit' Print the bit representation of numbers as stored in memory. For example, the value of `pi' is 01000000000010010010000111111011 01010100010001000010110100011000 (shown here in two 32 bit sections for typesetting purposes) when printed in bit format on a workstation which stores 8 byte real values in IEEE format with the least significant byte first. This format only works for numeric types. By default, Octave will try to print numbers with at least 5 significant figures within a field that is a maximum of 10 characters wide. If Octave is unable to format a matrix so that columns line up on the decimal point and all the numbers fit within the maximum field width, it switches to an `e' format. If `format' is invoked without any options, the default format state is restored. - Built-in Variable: print_answer_id_name If the value of `print_answer_id_name' is nonzero, variable names are printed along with the result. Otherwise, only the result values are printed. The default value is 1. File: octave, Node: Terminal Input, Next: Simple File I/O, Prev: Terminal Output, Up: Basic Input and Output Terminal Input -------------- Octave has three functions that make it easy to prompt users for input. The `input' and `menu' functions are normally used for managing an interactive dialog with a user, and the `keyboard' function is normally used for doing simple debugging. - Built-in Function: input (PROMPT) - Built-in Function: input (PROMPT, "s") Print a prompt and wait for user input. For example, input ("Pick a number, any number! ") prints the prompt Pick a number, any number! and waits for the user to enter a value. The string entered by the user is evaluated as an expression, so it may be a literal constant, a variable name, or any other valid expression. Currently, `input' only returns one value, regardless of the number of values produced by the evaluation of the expression. If you are only interested in getting a literal string value, you can call `input' with the character string `"s"' as the second argument. This tells Octave to return the string entered by the user directly, without evaluating it first. Because there may be output waiting to be displayed by the pager, it is a good idea to always call `fflush (stdout)' before calling `input'. This will ensure that all pending output is written to the screen before your prompt. *Note Input and Output::. - Function File: menu (TITLE, OPT1, ...) Print a title string followed by a series of options. Each option will be printed along with a number. The return value is the number of the option selected by the user. This function is useful for interactive programs. There is no limit to the number of options that may be passed in, but it may be confusing to present more than will fit easily on one screen. - Built-in Function: keyboard (PROMPT) This function is normally used for simple debugging. When the `keyboard' function is executed, Octave prints a prompt and waits for user input. The input strings are then evaluated and the results are printed. This makes it possible to examine the values of variables within a function, and to assign new values to variables. No value is returned from the `keyboard' function, and it continues to prompt for input until the user types `quit', or `exit'. If `keyboard' is invoked without any arguments, a default prompt of `debug> ' is used. For both `input' and `keyboard', the normal command line history and editing functions are available at the prompt. Octave also has a function that makes it possible to get a single character from the keyboard without requiring the user to type a carriage return. - Built-in Function: kbhit () Read a single keystroke from the keyboard. For example, x = kbhit (); will set X to the next character typed at the keyboard as soon as it is typed. File: octave, Node: Simple File I/O, Prev: Terminal Input, Up: Basic Input and Output Simple File I/O --------------- The `save' and `load' commands allow data to be written to and read from disk files in various formats. The default format of files written by the `save' command can be controlled using the built-in variables `default_save_format' and `save_precision'. Note that Octave can not yet save or load structure variables or any user-defined types. - Command: save OPTIONS FILE V1 V2 ... Save the named variables V1, V2, ... in the file FILE. The special filename `-' can be used to write the output to your terminal. If no variable names are listed, Octave saves all the variables in the current scope. Valid options for the `save' command are listed in the following table. Options that modify the output format override the format specified by the built-in variable `default_save_format'. `-ascii' Save the data in Octave's text data format. `-binary' Save the data in Octave's binary data format. `-float-binary' Save the data in Octave's binary data format but only using single precision. You should use this format only if you know that all the values to be saved can be represented in single precision. `-mat-binary' Save the data in MATLAB's binary data format. `-save-builtins' Force Octave to save the values of built-in variables too. By default, Octave does not save built-in variables. The list of variables to save may include wildcard patterns containing the following special characters: `?' Match any single character. `*' Match zero or more characters. `[ LIST ]' Match the list of characters specified by LIST. If the first character is `!' or `^', match all characters except those specified by LIST. For example, the pattern `[a-zA-Z]' will match all lower and upper case alphabetic characters. Except when using the MATLAB binary data file format, saving global variables also saves the global status of the variable, so that if it is restored at a later time using `load', it will be restored as a global variable. The command save -binary data a b* saves the variable `a' and all variables beginning with `b' to the file `data' in Octave's binary format. There are two variables that modify the behavior of `save' and one that controls whether variables are saved when Octave exits unexpectedly. - Built-in Variable: crash_dumps_octave_core If this variable is set to a nonzero value, Octave tries to save all current variables the the file "octave-core" if it crashes or receives a hangup, terminate or similar signal. The default value is 1. - Built-in Variable: default_save_format This variable specifies the default format for the `save' command. It should have one of the following values: `"ascii"', `"binary"', `float-binary', or `"mat-binary"'. The initial default save format is Octave's text format. - Built-in Variable: save_precision This variable specifies the number of digits to keep when saving data in text format. The default value is 17. - Command: load OPTIONS FILE V1 V2 ... Load the named variables from the file FILE. As with `save', you may specify a list of variables and `load' will only extract those variables with names that match. For example, to restore the variables saved in the file `data', use the command load data Octave will refuse to overwrite existing variables unless you use the option `-force'. If a variable that is not marked as global is loaded from a file when a global symbol with the same name already exists, it is loaded in the global symbol table. Also, if a variable is marked as global in a file and a local symbol exists, the local symbol is moved to the global symbol table and given the value from the file. Since it seems that both of these cases are likely to be the result of some sort of error, they will generate warnings. The `load' command can read data stored in Octave's text and binary formats, and MATLAB's binary format. It will automatically detect the type of file and do conversion from different floating point formats (currently only IEEE big and little endian, though other formats may added in the future). Valid options for `load' are listed in the following table. `-force' Force variables currently in memory to be overwritten by variables with the same name found in the file. `-ascii' Force Octave to assume the file is in Octave's text format. `-binary' Force Octave to assume the file is in Octave's binary format. `-mat-binary' Force Octave to assume the file is in MATLAB's binary format. File: octave, Node: C-Style I/O Functions, Prev: Basic Input and Output, Up: Input and Output C-Style I/O Functions ===================== Octave's C-style input and output functions provide most of the functionality of the C programming language's standard I/O library. The argument lists for some of the input functions are slightly different, however, because Octave has no way of passing arguments by reference. In the following, FILE refers to a file name and `fid' refers to an integer file number, as returned by `fopen'. There are three files that are always available. Although these files can be accessed using their corresponding numeric file ids, you should always use the symbolic names given in the table below, since it will make your programs easier to understand. - Built-in Variable: stdin The standard input stream (file id 0). When Octave is used interactively, this is filtered through the command line editing functions. - Built-in Variable: stdout The standard output stream (file id 1). Data written to the standard output is normally filtered through the pager. - Built-in Variable: stderr The standard error stream (file id 2). Even if paging is turned on, the standard error is not sent to the pager. It is useful for error messages and prompts. * Menu: * Opening and Closing Files:: * Simple Output:: * Line-Oriented Input:: * Formatted Output:: * Output Conversion for Matrices:: * Output Conversion Syntax:: * Table of Output Conversions:: * Integer Conversions:: * Floating-Point Conversions:: Other Output Conversions:: * Other Output Conversions:: * Formatted Input:: * Input Conversion Syntax:: * Table of Input Conversions:: * Numeric Input Conversions:: * String Input Conversions:: * Binary I/O:: * Temporary Files:: * EOF and Errors:: * File Positioning:: File: octave, Node: Opening and Closing Files, Next: Simple Output, Prev: C-Style I/O Functions, Up: C-Style I/O Functions Opening and Closing Files ------------------------- - Built-in Function: [FID, MSG] = fopen (NAME, MODE, ARCH) - Built-in Function: FID_LIST = fopen ("all") - Built-in Function: FILE = fopen (FID) The first form of the `fopen' function opens the named file with the specified mode (read-write, read-only, etc.) and architecture interpretation (IEEE big endian, IEEE little endian, etc.), and returns an integer value that may be used to refer to the file later. If an error occurs, FID is set to -1 and MSG contains the corresponding system error message. The MODE is a one or two character string that specifies whether the file is to be opened for reading, writing, or both. The second form of the `fopen' function returns a vector of file ids corresponding to all the currently open files, excluding the `stdin', `stdout', and `stderr' streams. The third form of the `fopen' function returns the name of a currently open file given its file id. For example, myfile = fopen ("splat.dat", "r", "ieee-le"); opens the file `splat.dat' for reading. If necessary, binary numeric values will be read assuming they are stored in IEEE format with the least significant bit first, and then converted to the native representation. Opening a file that is already open simply opens it again and returns a separate file id. It is not an error to open a file several times, though writing to the same file through several different file ids may produce unexpected results. The possible values `mode' may have are `r' Open a file for reading. `w' Open a file for writing. The previous contents are discared. `a' Open or create a file for writing at the end of the file. `r+' Open an existing file for reading and writing. `w+' Open a file for reading or writing. The previous contents are discarded. `a+' Open or create a file for reading or writing at the end of the file. The parameter ARCH is a string specifying the default data format for the file. Valid values for ARCH are: `native' The format of the current machine (this is the default). `ieee-le' IEEE big endian format. `ieee-be' IEEE little endian format. `vaxd' VAX D floating format. `vaxg' VAX G floating format. `cray' Cray floating format. however, conversions are currently only supported for `native' `ieee-be', and `ieee-le' formats. - Built-in Function: fclose (FID) Closes the specified file. If an error is encountered while trying to close the file, an error message is printed and `fclose' returns 0. Otherwise, it returns 1. File: octave, Node: Simple Output, Next: Line-Oriented Input, Prev: Opening and Closing Files, Up: C-Style I/O Functions Simple Output ------------- - Built-in Function: fputs (FID, STRING) Write a string to a file with no formatting. - Function File: puts (STRING) Write a string to the standard output with no formatting. File: octave, Node: Line-Oriented Input, Next: Formatted Output, Prev: Simple Output, Up: C-Style I/O Functions Line-Oriented Input ------------------- - Built-in Function: fgetl (FID, LEN) Read characters from a file, stopping after a newline, or EOF, or LEN characters have been read. The characters read, excluding the possible trailing newline, are returned as a string. If LEN is omitted, `fgetl' reads until the next newline character. If there are no more characters to read, `fgetl' returns -1. - Built-in Function: fgets (FID, LEN) Read characters from a file, stopping after a newline, or EOF, or LEN characters have been read. The characters read, including the possible trailing newline, are returned as a string. If LEN is omitted, `fgets' reads until the next newline character. If there are no more characters to read, `fgets' returns -1. File: octave, Node: Formatted Output, Next: Output Conversion for Matrices, Prev: Line-Oriented Input, Up: C-Style I/O Functions Formatted Output ---------------- This section describes how to call `printf' and related functions. The following functions are available for formatted output. They are modelled after the C language functions of the same name, but they interpret the format template differently in order to improve the performance of printing vector and matrix values. - Function File: printf (TEMPLATE, ...) The `printf' function prints the optional arguments under the control of the template string TEMPLATE to the stream `stdout'. - Built-in Function: fprintf (FID, TEMPLATE, ...) This function is just like `printf', except that the output is written to the stream FID instead of `stdout'. - Built-in Function: sprintf (TEMPLATE, ...) This is like `printf', except that the output is returned as a string. Unlike the C library function, which requires you to provide a suitably sized string as an argument, Octave's `sprintf' function returns the string, automatically sized to hold all of the items converted. The `printf' function can be used to print any number of arguments. The template string argument you supply in a call provides information not only about the number of additional arguments, but also about their types and what style should be used for printing them. Ordinary characters in the template string are simply written to the output stream as-is, while "conversion specifications" introduced by a `%' character in the template cause subsequent arguments to be formatted and written to the output stream. For example, pct = 37; filename = "foo.txt"; printf ("Processing of `%s' is %d%% finished.\nPlease be patient.\n", filename, pct); produces output like Processing of `foo.txt' is 37% finished. Please be patient. This example shows the use of the `%d' conversion to specify that a scalar argument should be printed in decimal notation, the `%s' conversion to specify printing of a string argument, and the `%%' conversion to print a literal `%' character. There are also conversions for printing an integer argument as an unsigned value in octal, decimal, or hexadecimal radix (`%o', `%u', or `%x', respectively); or as a character value (`%c'). Floating-point numbers can be printed in normal, fixed-point notation using the `%f' conversion or in exponential notation using the `%e' conversion. The `%g' conversion uses either `%e' or `%f' format, depending on what is more appropriate for the magnitude of the particular number. You can control formatting more precisely by writing "modifiers" between the `%' and the character that indicates which conversion to apply. These slightly alter the ordinary behavior of the conversion. For example, most conversion specifications permit you to specify a minimum field width and a flag indicating whether you want the result left- or right-justified within the field. The specific flags and modifiers that are permitted and their interpretation vary depending on the particular conversion. They're all described in more detail in the following sections. File: octave, Node: Output Conversion for Matrices, Next: Output Conversion Syntax, Prev: Formatted Output, Up: C-Style I/O Functions Output Conversion for Matrices ------------------------------ When given a matrix value, Octave's formatted output functions cycle through the format template until all the values in the matrix have been printed. For example, printf ("%4.2f %10.2e %8.4g\n", hilb (3)); -| 1.00 5.00e-01 0.3333 -| 0.50 3.33e-01 0.25 -| 0.33 2.50e-01 0.2 If more than one value is to be printed in a single call, the output functions do not return to the beginning of the format template when moving on from one value to the next. This can lead to confusing output if the number of elements in the matrices are not exact multiples of the number of conversions in the format template. For example, printf ("%4.2f %10.2e %8.4g\n", [1, 2], [3, 4]); -| 1.00 2.00e+00 3 -| 4.00 If this is not what you want, use a series of calls instead of just File: octave, Node: Output Conversion Syntax, Next: Table of Output Conversions, Prev: Output Conversion for Matrices, Up: C-Style I/O Functions Output Conversion Syntax ------------------------ This section provides details about the precise syntax of conversion specifications that can appear in a `printf' template string. Characters in the template string that are not part of a conversion specification are printed as-is to the output stream. The conversion specifications in a `printf' template string have the general form: % FLAGS WIDTH [ . PRECISION ] TYPE CONVERSION For example, in the conversion specifier `%-10.8ld', the `-' is a flag, `10' specifies the field width, the precision is `8', the letter `l' is a type modifier, and `d' specifies the conversion style. (This particular type specifier says to print a numeric argument in decimal notation, with a minimum of 8 digits left-justified in a field at least 10 characters wide.) In more detail, output conversion specifications consist of an initial `%' character followed in sequence by: * Zero or more "flag characters" that modify the normal behavior of the conversion specification. * An optional decimal integer specifying the "minimum field width". If the normal conversion produces fewer characters than this, the field is padded with spaces to the specified width. This is a *minimum* value; if the normal conversion produces more characters than this, the field is *not* truncated. Normally, the output is right-justified within the field. You can also specify a field width of `*'. This means that the next argument in the argument list (before the actual value to be printed) is used as the field width. The value is rounded to the nearest integer. If the value is negative, this means to set the `-' flag (see below) and to use the absolute value as the field width. * An optional "precision" to specify the number of digits to be written for the numeric conversions. If the precision is specified, it consists of a period (`.') followed optionally by a decimal integer (which defaults to zero if omitted). You can also specify a precision of `*'. This means that the next argument in the argument list (before the actual value to be printed) is used as the precision. The value must be an integer, and is ignored if it is negative. * An optional "type modifier character". This character is ignored by Octave's `printf' function, but is recognized to provide compatibility with the C language `printf'. * A character that specifies the conversion to be applied. The exact options that are permitted and how they are interpreted vary between the different conversion specifiers. See the descriptions of the individual conversions for information about the particular options that they use. File: octave, Node: Table of Output Conversions, Next: Integer Conversions, Prev: Output Conversion Syntax, Up: C-Style I/O Functions Table of Output Conversions --------------------------- Here is a table summarizing what all the different conversions do: `%d', `%i' Print an integer as a signed decimal number. *Note Integer Conversions::, for details. `%d' and `%i' are synonymous for output, but are different when used with `scanf' for input (*note Table of Input Conversions::.). Print an integer as an unsigned octal number. *Note Integer Conversions::, for details. Print an integer as an unsigned decimal number. *Note Integer Conversions::, for details. `%x', `%X' Print an integer as an unsigned hexadecimal number. `%x' uses lower-case letters and `%X' uses upper-case. *Note Integer Conversions::, for details. Print a floating-point number in normal (fixed-point) notation. *Note Floating-Point Conversions::, for details. `%e', `%E' Print a floating-point number in exponential notation. `%e' uses lower-case letters and `%E' uses upper-case. *Note Floating-Point Conversions::, for details. `%g', `%G' Print a floating-point number in either normal (fixed-point) or exponential notation, whichever is more appropriate for its magnitude. `%g' uses lower-case letters and `%G' uses upper-case. *Note Floating-Point Conversions::, for details. Print a single character. *Note Other Output Conversions::. Print a string. *Note Other Output Conversions::. Print a literal `%' character. *Note Other Output Conversions::. If the syntax of a conversion specification is invalid, unpredictable things will happen, so don't do this. If there aren't enough function arguments provided to supply values for all the conversion specifications in the template string, or if the arguments are not of the correct types, the results are unpredictable. If you supply more arguments than conversion specifications, the extra argument values are simply ignored; this is sometimes useful.