This is Info file oct-faq, produced by Makeinfo-1.64 from the input
file oct-faq.tex.


File: oct-faq,  Node: Top,  Next: What is Octave?,  Prev: (dir),  Up: (dir)



Preface
*******

   This is a list of frequently asked questions (FAQ) for Octave users.

   Some information in this FAQ was written for earlier versions of
Octave and may now be obsolete.

   I'm looking for new questions (*with* answers), better answers, or
both.  Please send suggestions to bug-octave@bevo.che.wisc.edu.  If you
have general questions about Octave, or need help for something that is
not covered by the Octave manual or the FAQ, please use the
help-octave@bevo.che.wisc.edu mailing list.

   This FAQ is intended to supplement, not replace, the Octave manual.
Before posting a question to the help-octave mailing list, you should
first check to see if the topic is covered in the manual.

* Menu:

* What is Octave?::
* Version 2.0::
* Octave Features::
* Documentation::
* Getting Octave::
* Installation::
* Common problems::
* Getting additional help::
* Bug reports::
* MATLAB compatibility::
* Index::


File: oct-faq,  Node: What is Octave?,  Next: Version 2.0,  Prev: Top,  Up: Top

What is Octave?
***************

   Octave is a high-level interactive language, primarily intended for
numerical computations that is mostly compatible with MATLAB.(1)

   Octave can do arithmetic for real and complex scalars and matrices,
solve sets of nonlinear algebraic equations, integrate functions over
finite and infinite intervals, and integrate systems of ordinary
differential and differential-algebraic equations.

   Octave uses the GNU readline library to handle reading and editing
input.  By default, the line editing commands are similar to the cursor
movement commands used by GNU Emacs, and a vi-style line editing
interface is also available.  At the end of each session, the command
history is saved, so that commands entered during previous sessions are
not lost.

   The Octave distribution includes a 200+ page Texinfo manual.  Access
to the complete text of the manual is available via the help command at
the Octave prompt.

   Two and three dimensional plotting is fully supported using gnuplot.

   The underlying numerical solvers are currently standard Fortran ones
like Lapack, Linpack, Odepack, the Blas, etc., packaged in a library of
C++ classes.  If possible, the Fortran subroutines are compiled with
the system's Fortran compiler, and called directly from the C++
functions.  If that's not possible, you can still compile Octave if you
have the free Fortran to C translator f2c.

   Octave is also free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by the
Free Software Foundation.

   ---------- Footnotes ----------

   (1)  MATLAB is a registered trademark of The MathWorks, Inc.


File: oct-faq,  Node: Version 2.0,  Next: Octave Features,  Prev: What is Octave?,  Up: Top

What's new in version 2.0 of Octave
***********************************

   Version 2.0.10 of Octave was released February 6, 1998.  Most bugs
reported since version 2.0 was release have been fixed, and a number of
new features have been added.  Octave is now much more compatible with
MATLAB.

   A list of user-visible changes in recent versions of Octave may be
found in the file NEWS, distributed in both source and binary releases
of Octave.


File: oct-faq,  Node: Octave Features,  Next: Documentation,  Prev: Version 2.0,  Up: Top

What features are unique to Octave?
***********************************

* Menu:

* Command and variable name completion::
* Command history::
* Data structures::
* Short-circuit boolean operators::
* Increment and decrement operators::
* Unwind-protect::
* Variable-length argument lists::
* Variable-length return lists::
* Built-in ODE and DAE solvers::


File: oct-faq,  Node: Command and variable name completion,  Next: Command history,  Prev: Octave Features,  Up: Octave Features

Command and variable name completion
====================================

   Typing a TAB character (ASCII code 9) on the command line causes
Octave to attempt to complete variable, function, and file names.
Octave uses the text before the cursor as the initial portion of the
name to complete.

   For example, if you type `fu' followed by TAB at the Octave prompt,
Octave will complete the rest of the name `function' on the command
line (unless you have other variables or functions defined that begin
with the characters `fu').  If there is more than one possible
completion, Octave will ring the terminal bell to let you know that your
initial sequence of characters is not enough to specify a unique name.
To complete the name, you may either edit the initial character sequence
(usually adding more characters until completion is possible) or type
another TAB to cause Octave to display the list of possible completions.


File: oct-faq,  Node: Command history,  Next: Data structures,  Prev: Command and variable name completion,  Up: Octave Features

Command history
===============

   When running interactively, Octave saves the commands you type in an
internal buffer so that you can recall and edit them.  Emacs and vi
editing modes are available with Emacs keybindings enabled by default.

   When Octave exits, the current command history is saved to the file
`~/.octave_hist', and each time Octave starts, it inserts the contents
of the `~/.octave_hist' file in the history list so that it is easy to
begin working where you left off.


File: oct-faq,  Node: Data structures,  Next: Short-circuit boolean operators,  Prev: Command history,  Up: Octave Features

Data structures
===============

   Octave includes a limited amount of support for organizing data in
structures.  The current implementation uses an associative array with
indices limited to strings, but the syntax is more like C-style
structures.  Here are some examples of using data structures in Octave.

   * Elements of structures can be of any value type.

          octave:1> x.a = 1; x.b = [1, 2; 3, 4]; x.c = "string";
          octave:2> x.a
          x.a = 1
          octave:3> x.b
          x.b =
          
            1  2
            3  4
          
          octave:4> x.c
          x.c = string

   * Structures may be copied.

          octave:1> y = x
          y =
          {
            a = 1
            b =
          
              1  2
              3  4
          
            c = string
            s =
          
              0.00000  0.00000  0.00000
              0.00000  5.46499  0.00000
              0.00000  0.00000  0.36597
          
            u =
          
              -0.40455  -0.91451
              -0.91451   0.40455
          
            v =
          
              -0.57605   0.81742
              -0.81742  -0.57605
          }

   * Structure elements may reference other structures.

          octave:1> x.b.d = 3
          x.b.d = 3
          octave:2> x.b
          ans =
          {
            d = 3
          }
          octave:3> x.b.d
          ans = 3

   * Functions can return structures.

          octave:1> function y = f (x)
          > y.re = real (x);
          > y.im = imag (x);
          > endfunction
          
          octave:2> f (rand + rand*I);
          ans =
          {
            im = 0.18033
            re = 0.19069
          }

   * Function return lists can include structure elements, and they may
     be indexed like any other variable.

          octave:1> [x.u, x.s(2:3,2:3), x.v] = svd ([1, 2; 3, 4]);
          octave:2> x
          x =
          {
            s =
          
              0.00000  0.00000  0.00000
              0.00000  5.46499  0.00000
              0.00000  0.00000  0.36597
          
            u =
          
              -0.40455  -0.91451
              -0.91451   0.40455
          
            v =
          
              -0.57605   0.81742
              -0.81742  -0.57605
          }

   * You can also use the function `is_struct' to determine whether a
     given value is a data structure.  For example

          is_struct (x)

     returns 1 if the value of the variable X is a data structure.

   This feature should be considered experimental, but you should
expect it to work.  Suggestions for ways to improve it are welcome.


File: oct-faq,  Node: Short-circuit boolean operators,  Next: Increment and decrement operators,  Prev: Data structures,  Up: Octave Features

Short-circuit boolean operators
===============================

   Octave's `&&' and `||' logical operators are evaluated in a
short-circuit fashion (like the corresponding operators in the C
language) and work differently than the element by element operators
`&' and `|'.


File: oct-faq,  Node: Increment and decrement operators,  Next: Unwind-protect,  Prev: Short-circuit boolean operators,  Up: Octave Features

Increment and decrement operators
=================================

   Octave includes the C-like increment and decrement operators `++'
and `--' in both their prefix and postfix forms.

   For example, to pre-increment the variable X, you would write `++X'.
This would add one to X and then return the new value of X as the
result of the expression.  It is exactly the same as the expression `X
= X + 1'.

   To post-increment a variable X, you would write `X++'.  This adds
one to the variable X, but returns the value that X had prior to
incrementing it.  For example, if X is equal to 2, the result of the
expression `X++' is 2, and the new value of X is 3.

   For matrix and vector arguments, the increment and decrement
operators work on each element of the operand.

   It is not currently possible to increment index expressions.  For
example, you might expect that the expression `V(4)++' would increment
the fourth element of the vector V, but instead it results in a parse
error.  This problem may be fixed in a future release of Octave.


File: oct-faq,  Node: Unwind-protect,  Next: Variable-length argument lists,  Prev: Increment and decrement operators,  Up: Octave Features

Unwind-protect
==============

   Octave supports a limited form of exception handling modelled after
the unwind-protect form of Lisp.  The general form of an
`unwind_protect' block looks like this:

     unwind_protect
       BODY
     unwind_protect_cleanup
       CLEANUP
     end_unwind_protect

Where BODY and CLEANUP are both optional and may contain any Octave
expressions or commands.  The statements in CLEANUP are guaranteed to
be executed regardless of how control exits BODY.

   The `unwind_protect' statement is often used to reliably restore the
values of global variables that need to be temporarily changed.


File: oct-faq,  Node: Variable-length argument lists,  Next: Variable-length return lists,  Prev: Unwind-protect,  Up: Octave Features

Variable-length argument lists
==============================

   Octave has a real mechanism for handling functions that take an
unspecified number of arguments, so it is no longer necessary to place
an upper bound on the number of optional arguments that a function can
accept.

   Here is an example of a function that uses the new syntax to print a
header followed by an unspecified number of values:

     function foo (heading, ...)
       disp (heading);
       va_start ();
       while (--nargin)
         disp (va_arg ());
       endwhile
     endfunction

   Calling `va_start()' positions an internal pointer to the first
unnamed argument and allows you to cycle through the arguments more than
once.  It is not necessary to call `va_start()' if you do not plan to
cycle through the arguments more than once.

   The function `va_arg()' returns the value of the next available
argument and moves the internal pointer to the next argument.  It is an
error to call `va_arg()' when there are no more arguments available.

   It is also possible to use the keyword ALL_VA_ARGS to pass all
unnamed arguments to another function.


File: oct-faq,  Node: Variable-length return lists,  Next: Built-in ODE and DAE solvers,  Prev: Variable-length argument lists,  Up: Octave Features

Variable-length return lists
============================

   Octave also has a real mechanism for handling functions that return
an unspecified number of values, so it is no longer necessary to place
an upper bound on the number of outputs that a function can produce.

   Here is an example of a function that uses the new syntax to produce
`N' values:

     function [...] = foo (n)
       for i = 1:n
         vr_val (i);
       endfor
     endfunction


File: oct-faq,  Node: Built-in ODE and DAE solvers,  Prev: Variable-length return lists,  Up: Octave Features

Built-in ODE and DAE solvers
============================

   Octave includes LSODE and DASSL for solving systems of stiff ordinary
differential and differential-algebraic equations.  These functions are
built in to the interpreter.


File: oct-faq,  Node: Documentation,  Next: Getting Octave,  Prev: Octave Features,  Up: Top

What documentation exists for Octave?
*************************************

   The Octave distribution includes a 220+ page manual that is also
distributed under the terms of the GNU GPL.

   The Octave manual is intended to be a complete reference for Octave,
but it is not a finished document.  If you have problems using it, or
find that some topic is not adequately explained, indexed, or
cross-referenced, please send a bug report to
bug-octave@bevo.che.wisc.edu.

   Because the Octave manual is written using Texinfo, the complete
text of the Octave manual is also available on line using the GNU Info
system via the GNU Emacs, info, or xinfo programs, or by using the
`help -i' command to start the GNU info browser directly from the
Octave prompt.

   It is also possible to use your favorite WWW browser to read the
Octave manual by converting the Texinfo source to HTML using the
`texi2html' program.


File: oct-faq,  Node: Getting Octave,  Next: Installation,  Prev: Documentation,  Up: Top

Obtaining Source Code
*********************

* Menu:

* Octave for Unix::
* Octave for other platforms::
* latest versions::


File: oct-faq,  Node: Octave for Unix,  Next: Octave for other platforms,  Prev: Getting Octave,  Up: Getting Octave

How do I get a copy of Octave for Unix?
=======================================

   You can get Octave from a friend who has a copy, by anonymous FTP,
or by ordering a tape or CD-ROM from the Free Software Foundation (FSF).

   Octave was not developed by the FSF, but the FSF does distribute
Octave, and the developers of Octave support the efforts of the FSF by
encouraging users of Octave to order Octave on CD-ROM directly from the
FSF.

   The FSF is a nonprofit organization that distributes software and
manuals to raise funds for more GNU development.  Buying a CD-ROM from
the FSF contributes directly to paying staff to develop GNU software.
CD-ROMs cost $240 if an organization is buying, or $60 if an individual
is buying.

   For more information about ordering from the FSF, contact
gnu@gnu.org, phone (617) 542-5942 or anonymous ftp the file
`/pub/gnu/GNUinfo/ORDERS' from ftp.gnu.org.

   If you are on the Internet, you can copy the latest distribution
version of Octave from the file `/pub/octave/octave-M.N.tar.gz', on the
host `ftp.che.wisc.edu'.  This tar file has been compressed with GNU
gzip, so be sure to use binary mode for the transfer.  `M' and `N'
stand for version numbers; look at a listing of the directory through
ftp to see what version is available.  After you unpack the
distribution, be sure to look at the files `README' and `INSTALL'.

   Binaries for several popular systems are also available.  If you
would like help out by making binaries available for other systems,
please contact bug-octave@bevo.che.wisc.edu.

   A list of user-visible changes since the last release is available in
the file `NEWS'.  The file `ChangeLog' in the source distribution
contains a more detailed record of changes made since the last release.


File: oct-faq,  Node: Octave for other platforms,  Next: latest versions,  Prev: Octave for Unix,  Up: Getting Octave

How do I get a copy of Octave for (some other platform)?
========================================================

   Octave currently runs on Unix-like systems, OS/2, and Windows NT/95
(using the gnu-win32 tools from Cygnus Support).  It should be possible
to make Octave work on other systems as well.  If you are interested in
porting Octave to other systems, please contact
bug-octave@bevo.che.wisc.edu.


File: oct-faq,  Node: latest versions,  Prev: Octave for other platforms,  Up: Getting Octave

What is the latest version of Octave
====================================

   The latest version of Octave is 2.0.10, released February 6, 1998.


File: oct-faq,  Node: Installation,  Next: Common problems,  Prev: Getting Octave,  Up: Top

Installation Issues and Problems
********************************

   Octave requires approximately 125MB of disk storage to unpack and
compile from source (significantly less if you don't compile with
debugging symbols or create shared libraries).  Once installed, Octave
requires approximately 65MB of disk space (again, considerably less if
you don't build shared libraries or the binaries and libraries do not
include debugging symbols).

* Menu:

* What else do I need?::
* Other C++ compilers?::


File: oct-faq,  Node: What else do I need?,  Next: Other C++ compilers?,  Prev: Installation,  Up: Installation

What else do I need?
====================

   To compile Octave, you will need a recent version of GNU Make.  You
will also need g++ 2.7.2 or later.  Version 2.8.0 or egcs 1.0.x should
work.  Later versions may work, but C++ is still evolving, so don't be
too surprised if you run into some trouble.

   It is no longer necessary to have libg++, but you do need to have the
GNU implementation of libstdc++.  If you are using g++ 2.7.2, libstdc++
is distributed along with libg++, but for later versions, libstdc++ is
distributed separately.  For egcs, libstdc++ is included with the
compiler distribution.

   <em>You must have gnu make to compile octave</em>.  Octave's
Makefiles use features of GNU Make that are not present in other
versions of make.  GNU Make is very portable and easy to install.


File: oct-faq,  Node: Other C++ compilers?,  Prev: What else do I need?,  Up: Installation

Can I compile Octave with another C++ compiler?
===============================================

   Currently, Octave can only be compiled with the GNU C++ compiler.  It
would be nice to make it possible to compile Octave with other C++
compilers, but the maintainers do not have sufficient time to devote to
this.  If you are interested in working to make Octave portable to other
compilers, please contact bug-octave@bevo.che.wisc.edu.


File: oct-faq,  Node: Common problems,  Next: Getting additional help,  Prev: Installation,  Up: Top

Common problems
***************

   This list is probably far too short.  Feel free to suggest additional
questions (preferably with answers!)

   * Octave takes a long time to find symbols.

     Octave is probably spending this time recursively searching
     directories for function files.  Check the value of your LOADPATH.
     For those elements that end in `//', do any name a very large
     directory tree?  Does it contain directories that have a mixture
     of files and directories?  In order for the recursive directory
     searching code to work efficiently, directories that are to be
     searched recursively should have either function files only, or
     subdirectories only, but not a mixture of both.  Check to make
     sure that Octave's standard set of function files is installed
     this way.


File: oct-faq,  Node: Getting additional help,  Next: Bug reports,  Prev: Common problems,  Up: Top

Getting additional help
***********************

   The mailing list

     help-octave@bevo.che.wisc.edu

is available for questions related to using, installing, and porting
Octave that are not adequately answered by the Octave manual or by this
document.

   If you would like to join the discussion and receive all messages
sent to the list, please send a short note to

     help-octave-request@bevo.che.wisc.edu
                 ^^^^^^^

   *Please do not* send requests to be added or removed from the the
mailing list, or other administrative trivia to the list itself.

   An archive of old postings to the help-octave mailing list is
maintained on ftp.che.wisc.edu in the directory
`/pub/octave/MAILING-LISTS'.


File: oct-faq,  Node: Bug reports,  Next: MATLAB compatibility,  Prev: Getting additional help,  Up: Top

I think I have found a bug in Octave.
*************************************

   "I think I have found a bug in Octave, but I'm not sure.  How do I
know, and who should I tell?"

   First, see the section on bugs and bug reports in the Octave manual.
The Octave manual is included in the Octave distribution.

   When you report a bug, make sure to describe the type of computer you
are using, the version of the operating system it is running, and the
version of Octave that you are using.  Also provide enough code so that
the Octave maintainers can duplicate your bug.

   If you have Octave working at all, the easiest way to do this is to
use the Octave function `bug_report'.  When you execute this function,
Octave will prompt you for a subject and then invoke the editor on a
file that already contains all the configuration information.  When you
exit the editor, Octave will mail the bug report for you.

   If for some reason you cannot use Octave's `bug_report' function,
mail your bug report to "bug-octave@bevo.che.wisc.edu".  Your message
needs to include enough information to allow the maintainers of Octave
to fix the bug.  Please read the section on bugs and bug reports in the
Octave manual for a list of things that should be included in every bug
report.


File: oct-faq,  Node: MATLAB compatibility,  Next: Index,  Prev: Bug reports,  Up: Top

Porting programs from MATLAB to Octave
**************************************

   "I wrote some code for MATLAB, and I want to get it running under
Octave.  Is there anything I should watch out for?"

   The differences between Octave and MATLAB typically fall into one of
three categories:

  1. Irrelevant.

  2. Known differences, perhaps configurable with a user preference
     variable.

  3. Unknown differences.

   The first category, irrelevant differences, do not affect
computations and most likely do not affect the execution of function
files.

   The differences of the second category are usually because the
authors of Octave decided on a better (subjective) implementation that
the way MATLAB does it, and so introduced "user preference variables"
so that you can customize Octave's behavior to be either
MATLAB-compatible or to use Octave's new features.  To make Octave more
MATLAB-compatible, put the following statements in your `~/.octaverc'
file, or use the command line option `--traditional', which implies all
of these settings.  Note that this list may not be complete, because
some new variables may have been introduced since this document was
last updated.

       PS1 = ">> "
       PS2 = ""
       beep_on_error = 1.0
       default_eval_print_flag = 0.0
       default_save_format = "mat-binary"
       define_all_return_values = 1.0
       do_fortran_indexing = 1.0
       empty_list_elements_ok = 1.0
       fixed_point_format = 1.0
       implicit_num_to_str_ok = 1.0
       implicit_str_to_num_ok = 1.0
       ok_to_lose_imaginary_part = 1.0
       page_screen_output = 0.0
       prefer_column_vectors = 0.0
       prefer_zero_one_indexing = 1.0
       print_empty_dimensions = 0.0
       treat_neg_dim_as_zero = 1.0
       warn_function_name_clash = 0.0
       whitespace_in_literal_matrix = "traditional"

   Some other known differences are:

   * The Octave plotting functions are mostly compatible with the ones
     from MATLAB 3.x, but not from MATLAB 4.x.

   The third category of differences is (hopefully) shrinking.  If you
find a difference between Octave behavior and MATLAB, then you should
send a description of this difference (with code illustrating the
difference, if possible) to bug-octave@bevo.che.wisc.edu.

   An archive of old postings to the Octave mailing lists is maintained
on ftp.che.wisc.edu in the directory `/pub/octave/MAILING-LISTS'.


File: oct-faq,  Node: Index,  Prev: MATLAB compatibility,  Up: Top

Concept Index
*************

* Menu:

* MATLAB compatibility:                 MATLAB compatibility.
* Additional help:                      Getting additional help.
* Argument lists, variable-length:      Variable-length argument lists.
* Boolean operators, short-circuit:     Short-circuit boolean operators.
* Bug in Octave, newly found:           Bug reports.
* Command completion:                   Command and variable name completion.
* Command history:                      Command history.
* Compatibility with MATLAB:            MATLAB compatibility.
* DASSL:                                Built-in ODE and DAE solvers.
* Data structures:                      Data structures.
* Decrement operators:                  Increment and decrement operators.
* DJGPP:                                Octave for other platforms.
* EMX:                                  Octave for other platforms.
* FAQ for Octave, latest version:       Top.
* Flex:                                 What else do I need?.
* FSF [Free Software Foundation]:       Octave for Unix.
* FSF, contact <gnu@gnu.org>:           Octave for Unix.
* Function name completion:             Command and variable name completion.
* GNU Bison:                            What else do I need?.
* GNU g++:                              What else do I need?.
* GNU gcc:                              What else do I need?.
* GNU Make:                             What else do I need?.
* GNU [GNU's not unix]:                 Octave for Unix.
* GNUware, anonymous FTP sites:         Octave for Unix.
* History:                              Command history.
* Increment operators:                  Increment and decrement operators.
* libg++:                               What else do I need?.
* Logical operators, short-circuit:     Short-circuit boolean operators.
* LSODE:                                Built-in ODE and DAE solvers.
* Mailing lists, bug-octave:            Bug reports.
* Mailing lists, help-octave:           Getting additional help.
* Manual, for Octave:                   Bug reports.
* MS-DOS support:                       Octave for other platforms.
* Name completion:                      Command and variable name completion.
* Octave bug report:                    Bug reports.
* Octave, building:                     Installation.
* Octave, documentation:                Documentation.
* Octave, getting a copy:               Octave for Unix.
* Octave, ordering:                     Octave for Unix.
* Octave, version date:                 latest versions.
* Operators, boolean:                   Short-circuit boolean operators.
* Operators, decrement:                 Increment and decrement operators.
* Operators, increment:                 Increment and decrement operators.
* OS/2 support:                         Octave for other platforms.
* Return lists, variable-length:        Variable-length return lists.
* Short-circuit boolean operators:      Short-circuit boolean operators.
* Source code:                          Getting Octave.
* Structures:                           Data structures.
* Unwind-protect:                       Unwind-protect.
* Variable name completion:             Command and variable name completion.
* Variable-length argument lists:       Variable-length argument lists.
* Variable-length return lists:         Variable-length return lists.
* VAX:                                  Octave for other platforms.
* VMS support:                          Octave for other platforms.
* Windows support:                      Octave for other platforms.



Tag Table:
Node: Top87
Node: What is Octave?1097
Node: Version 2.02870
Node: Octave Features3413
Node: Command and variable name completion3864
Node: Command history4926
Node: Data structures5551
Node: Short-circuit boolean operators8346
Node: Increment and decrement operators8767
Node: Unwind-protect9963
Node: Variable-length argument lists10732
Node: Variable-length return lists12007
Node: Built-in ODE and DAE solvers12617
Node: Documentation12964
Node: Getting Octave13974
Node: Octave for Unix14193
Node: Octave for other platforms16083
Node: latest versions16613
Node: Installation16856
Node: What else do I need?17454
Node: Other C++ compilers?18372
Node: Common problems18905
Node: Getting additional help19833
Node: Bug reports20657
Node: MATLAB compatibility22042
Node: Index24541

End Tag Table
