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.

`io'
     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.


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 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.

   ---------- 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'
          This is the default format.  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.

    `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.

 - 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'.

 - 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.

 - Built-in Function:  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 at the first newline
     character that is encountered or after LEN characters have been
     read, and returning the characters as a string.  The newline is
     not included in the returned value.

     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 at the first newline
     character that is encountered or after LEN characters have been
     read, and returning the characters as a string.  The newline is
     included in the returned value.

     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
one.


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::.).

`%o'
     Print an integer as an unsigned octal number.  *Note Integer
     Conversions::, for details.

`%u'
     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.

`%f'
     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.

`%c'
     Print a single character.  *Note Other Output Conversions::.

`%s'
     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.

