GNU Octave

For other uses of the word octave see Octave (disambiguation)

GNU Octave

File:Octave Sombrero.jpg
GNU Octave with Octave Workshop GUI
Developer(s)	John W. Eaton
Repository	hg.savannah.gnu.org/hgweb/octave
Operating system	Windows, Linux, UNIX, Cygwin, Mac OS X
Type	Scientific computing
License	GNU General Public License
Website	http://www.octave.org/

Octave is a free computer program for performing numerical computations which is mostly compatible with MATLAB. It is part of the GNU project. Note that Octave is not a computer algebra system, but a tool for scientific computing.

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.

The name has nothing to do with musical octaves. It was the name of a former professor of one of the authors of Octave who was known for his ability to quickly come up with good approximations to numerical problems.

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 argument by reference.

Octave programs consist of a list of function calls or script. The language is matrix-based and provides various functions for matrix operation. 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) and work differently than 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 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

• 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 mainly built with MATLAB compatibility in mind. It essentially shares a lot of features in common 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.

Some of the differences that do exist between Octave and MATLAB can be worked around using "user preference variables."

See also

For a list of programs similar to GNU Octave, see the list of numerical analysis software.

External links

• Octave.org Home Page
• Octave Workshop: an Octave IDE
• kOctave: Graphical User Interface - for the KDE Desktop
• Online documentation
• Octave-forge community development page
• Octave wiki (click twice—page redirects cause some browsers to time out)
• Online access to Octave - Allows you to perform simple Octave calculation online.
• Octave FAQ Wiki with new plotting commands
• OctPlot A handle graphics package for Octave. It provides quality screen graphics.
• Help-Octave Mailing List Archives on Gmane Search Help-Octave Mailing lists.