GNU Octave

Octave is a free computer program for performing numerical computations which is mostly compatible with MATLAB. It is part of the GNU Project.

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 name has nothing to do with musical octaves. Octave is named after a former professor of the principal author, who was known for his ability to perform quick back-of-an-envelope calculations.

Technical details

• Octave is written in C++ using STL libraries.
• Octave has an interpreter that interprets the Octave language.
• Octave itself is extensible using dynamically loadable modules.
• Octave interpreter works in tandem 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 (an example of which is the C language) and supports many common C standard library constructs, and can be extended to support UNIX system calls and functions. However, it does not support passing arguments by reference.

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

Its syntax is very similar to MATLAB, and carefully programming a script will allow it to run on both Octave and MATLAB.

Because Octave is made available under the GNU General Public License, it may be freely copied and used. The program runs under most Unix and Unix-like operating systems, as well as Microsoft Windows.

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. 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
x.a = 1
octave:3> x.b
x.b =
 1  2
 3  4
octave:4> x.c
x.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: Octave includes the C-like increment and decrement operators `++' and `--' in both their prefix and postfix forms. Unwind-protect: Octave supports a limited form of exception handling modeled 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

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});
 endif
endfunction

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);
 endfor
endfunction

MATLAB compatibility

Octave has been built with MATLAB compatibility in mind. It therefore 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.

See also

• List of numerical analysis software
• Comparison of numerical analysis software

External links

• Octave.org Home Page

Documentation

• Online documentation
• Octave wiki (click twice—page redirects cause some browsers to time out)
• Octave FAQ Wiki with new plotting commands
• Mailing List Archives on Nabble - Search all Octave mailing lists.
• Mailing List Archives on Gmane - Search all Octave mailing lists.

Graphical User Interfaces

• QtOctave Graphical User Interface - Matlab counterpart. Under heavy Development.
• Octave Workshop: an Octave IDE - Development stopped in 2006
• kOctave: Graphical User Interface - for the KDE Desktop (base for Octave Workshop) Development stopped in 2003

Web Interfaces

• Web Interface to Octave - Computing using GNU Octave in webbrowser
• Online access to Octave - Allows you to perform simple Octave calculation online.

Add-ons

• Octave-forge community development page - Toolboxes for various problems from independent developers.
• OctPlot - High quality 2D graphics.
• Octave graphics add-on - 3D visualization system for Octave.
• Octaviz - 3D visualization system for Octave.
• MPI Toolbox for Octave (MPITB) - Parallel Computing for Octave using MPI.

References