GNU Octave

GNU Octave

GNU Octave screenshot
Developer(s)	John W. Eaton
Initial release	1988
Stable release	3.4.3  (October 10, 2011; 34 days ago (2011-10-10)) [+/−]
Preview release	3.3.54  (November 19, 2010; 11 months ago (2010-11-19))[1] [+/−]
Written in	C, C++
Platform	Cross-platform
Available in	19 languages
Type	Scientific computing
License	GNU General Public License
Website	gnu.org/software/octave/

GNU Octave is a high-level language, primarily intended for numerical computations. It provides a convenient command-line interface (CLI) for solving linear and nonlinear problems numerically, and for performing other numerical experiments using a language that is mostly compatible with MATLAB. It may also be used as a batch-oriented language. As part of the GNU Project, it is free software under the terms of the GNU General Public License (GPL).

History

The project was conceived around 1988. At first it was intended to be a companion to a chemical reactor design course. Real development was started by John W. Eaton in 1992. The first alpha release dates back to January 4, 1993 and on February 17, 1994 version 1.0 was released. Version 3.0 was released on December 21, 2007.

The program is named after Octave Levenspiel, a former professor of the principal author who was known for his ability to perform quick back-of-the-envelope calculations.^[2]

Deployments

In addition to use on desktops for personal scientific computing, Octave is used in academia and industry. For example, Octave was used on a massive parallel computer at Pittsburgh supercomputing center to find vulnerability related to guessing social security numbers.^[3]

Technical details

• Octave is written in C++ using the Standard Template Library (STL).
• Octave uses an interpreter to execute the Octave scripting language.
• Octave is extensible using dynamically loadable modules.
• Octave interpreter works with gnuplot and Grace software to create plots, graphs, and charts, and to save or print them.

Octave, the language

The Octave language is an interpreted programming language. It is a structured programming language (similar to C) and supports many common C standard library functions, and also certain UNIX system calls and functions.^[4] However, it does not support passing arguments by reference.^[5]

Octave programs consist of a list of function calls or a script. The syntax is matrix-based and provides various functions for matrix operations. It is not object-oriented, but it does support various data structures.

Its syntax is very similar to MATLAB, and careful programming of a script will allow it to run on both Octave and MATLAB.^[6]

Because Octave is made available under the GNU General Public License, it may be freely changed, copied and used.^[2] The program runs under most Unix and Unix-like operating systems, as well as Mac OS X and Microsoft Windows.^[7]

Notable features

Command and variable name completion

Typing a TAB character on the command line causes Octave to attempt to complete variable, function, and file names (similar to Bash's tab completion). Octave uses the text before the cursor as the initial portion of the name to complete.

Command history

When running interactively, Octave saves the commands typed in an internal buffer so that they can be recalled and edited.

Data structures

Octave includes a limited amount of support for organizing data in structures. For instance:

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

   1   2
   3   4

octave:4> x.c
ans = string
octave:5> x
x =
{
  a =  1
  b =

     1   2
     3   4

  c = string
}

Short-circuit boolean operators

Octave's '&&' and '||' logical operators are evaluated in a short-circuit fashion (like the corresponding operators in the C language), in contrast to the element-by-element operators '&' and '|'.

Increment and decrement operators

Main article: Increment and decrement operators

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

Unwind-protect

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

unwind_protect
   body
unwind_protect_cleanup
   cleanup
end_unwind_protect

As a general rule, GNU Octave recognizes as termination of a given 'block' either the keyword 'end' (which is compatible with the MATLAB language) or a more specific keyword 'end_block'. As a consequence, an 'unwind_protect' block can be terminated either with the keyword 'end_unwind_protect' as in the example, or with the more portable keyword 'end'.

The cleanup part of the block is always executed. In case an exception is raised by the body part, cleanup is executed immediately before propagating the exception outside the block 'unwind_protect'.

GNU Octave also supports another form of exception handling (compatible with the MATLAB language):

try
   body
catch
   exception_handling
end

This latter form differs from an 'unwind_protect' block in two ways. First, exception_handling is only executed when an exception is raised by body. Second, after the execution of exception_handling the exception is not propagated outside the block (unless a 'rethrow( lasterror )' statement is purposely inserted within the exception_handling code).

Variable-length argument lists

Octave has a real mechanism for handling functions that take an unspecified number of arguments without explicit upper limit. To specify a list of zero or more arguments, use the special argument varargin as the last (or only) argument in the list.

function s = plus (varargin)
   if (nargin==0)
      s = 0;
   else
      s = varargin{1} + plus (varargin{2:nargin});
   end
end

Variable-length return lists

A function can be set up to return any number of values by using the special return value varargout. For example:

function varargout = multiassign (data)
   for k=1:nargout
      varargout{k} = data(:,k);
   end
end

C++ integration

It is also possible to execute Octave code directly in a C++ program. For example, here is a code snippet for calling rand([10,1]):

#include <octave/oct.h>
...
ColumnVector NumRands(2);
NumRands(0) = 10;
NumRands(1) = 1;
octave_value_list f_arg, f_ret;
f_arg(0) = octave_value(NumRands);
f_ret = feval("rand",f_arg,1);
Matrix unis(f_ret(0).matrix_value());

MATLAB compatibility

Octave has been built with MATLAB compatibility in mind, and shares many features with MATLAB:

1. Matrices as fundamental data type.
2. Built-in support for complex numbers.
3. Powerful built-in math functions and extensive function libraries.
4. Extensibility in the form of user-defined functions.

There are a few purposeful, albeit minor, differences:

1. Comment lines can be prefixed with the # character as well as the % character
2. Various C-based operators ++, --, +=, *=, /= are supported
3. Elements can be referenced without creating a new variable, e.g. [1:10](3)
4. Strings can be defined with the " character as well as the ' character

See also

Free software portal

• List of numerical analysis software
• Comparison of numerical analysis software
• List of statistical packages
• List of numerical libraries

Further reading

• Hansen, Jesper (June 2011). GNU Octave Beginner's Guide. Packt Publishing.

External links

• Octave.org Home Page

Documentation

• Online documentation.
• Octave wiki (Click twice – page redirects cause some browsers to time out).
• Reviewed entry in the Free Software Directory.
• GNU Octave FAQ Wiki with new plotting commands^{[dead link]}
• Mailing List Archives on Nabble – Search all Octave mailing lists.
• Mailing List Archives on Gmane – Search all Octave mailing lists.
• Italian Octave Community.

Numerical packages and libraries interfacing with GNU Octave

GNU Octave is also powered by third-party tools and libraries, mostly providing general or domain-specific abstractions for scientific computing. Those tools may be categorized according whether their contributions are more oriented toward computational modelling or toward enhancing visual analysis.

Numerical tools

• Octave-forge community development page – Free software toolboxes for various problems from independent developers. A Windows installer for both GNU Octave and the toolboxes is also available.
• Mastrave project – Cross-language library (GNU GPLv3+ covered) compatible with GNU Octave and Matlab, to ease environmental modelling with general purpose semantic array programming utilities.
• Neuroimaging Analysis Kit – Library (MIT License covered) to process neuroimaging data within GNU Octave or Matlab, particularly functional magnetic resonance images. It also offers a Pipeline system to handle multi-stage processing.
• Parallel Matlab Toolbox – Matlab language data structures and functions which implement distributed Matlab arrays. It is released under MIT license.
• MPI Toolbox for Octave (MPITB) – Parallel Computing for Octave using MPI.

Plotting tools

• PLPlot – A replacement of the traditional gnuplot in GNU Octave, licensed under the GNU LGPL.
• OctPlot – High quality 2D graphics (postscript and screen graphics). Released under GNU GPL.
• Octave graphics add-on – 3D visualization system for Octave.
• Octaviz – 3D visualization system for GNU Octave (wrapper that makes VTK classes accessible from within GNU Octave). It also provides high-level functions for 2D visualization. (Note: Their site says, "Unfortunately, Octaviz is no longer in development. The latest release (0.4.7) was quite usable and stable when built against vtk-5.0.")

User interfaces

Octave does not come with a graphical user interface (GUI)/integrated development environment (IDE) by default. Instead, an additional graphical front-end must be installed.

Graphical user interfaces (GUI)

• An official graphical interface based on Qt has now been migrated to the main source repository and will likely be released with Octave 4.0.^{[citation needed]}
• GUIOctave (Windows) — GUIOctave provides a convenient Graphical User Interface to simplify the use of GNU Octave for user who don't like the original command line based version of GNU Octave, but still want to use the GNU Octave potential.
• Kalculus (Linux) — Matlab like UI for GNU Octave and Yacas written in Qt4 with Ruby bindings
• Xoctave (Windows, Linux) — Xoctave encapsulates GNU Octave using pipes and provides extra tools to make using it easier. Its UI is very similar to that of Matlab.
• OctaveNB — NetBeans IDE integration for GNU Octave (since 2009) - features SVN, local history, diff, multi language projects from the NetBeans IDE for your Octave development
• QtOctave Graphical User Interface (Windows, Linux) — A GUI with Matlab style.
• Cantor is a free software mathematics application for scientific statistics and analysis with built-in support for Octave. It is a part of the KDE project.

Web user interfaces (WUI)

• Online LaTeX and Octave Editor - Online Octave/Matlab editor with plotting and storage capabilities.
• Online access to Octave – Allows you to perform simple Octave calculations online.
• MathCloud – Share Matlab/Octave scripts and data and do your computations in the cloud.

References

1. ^ "Octave News Archive". http://www.gnu.org/software/octave/news.html. 
2. ^ ^{a b} Eaton, John W. "About Octave". http://www.gnu.org/software/octave/about.html. Retrieved 2009-06-28. 
3. ^ HPC, July 8, 2009.
4. ^ "GNU Octave - Controlling subprocesses". November 14, 2008. http://www.network-theory.co.uk/docs/octave3/octave_269.html. Retrieved Jan 28, 2009. 
5. ^ "GNU Octave". http://www.delorie.com/gnu/docs/octave/octave_105.html. Retrieved Jan 28, 2009. 
6. ^ "FAQ: MATLAB compatibility". http://www.gnu.org/software/octave/FAQ.html#MATLAB-compatibility. Retrieved July 4, 2009. 
7. ^ "FAQ: Getting Octave". http://www.gnu.org/software/octave/FAQ.html#Getting-Octave. Retrieved July 4, 2009.