GNU Octave

GNU Octave

GNU Octave 4.0.0 RC1 running on Linux
Developer(s)	John W. Eaton and many others
Initial release	1988 (1988)
Stable release	4.0.0 (May 29, 2015 (2015-05-29)) [±]
Preview release	4.0.0 rc4 (April 29, 2015 (2015-04-29)) [±]
Written in	C, C++, Fortran
Available in	19 languages
Type	Scientific computing
License	GPL
Website	gnu.org/software/octave/

GNU Octave is software featuring a high-level programming language, primarily intended for numerical computations. It provides a command-line interface 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. It is part of the GNU Project, it is free software under the terms of the GNU General Public License.

Octave is one of the two major free alternatives to MATLAB, the other one being Scilab. Scilab however puts less emphasis on (bidirectional) syntactic compatibility with MATLAB than Octave does.

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 4.0.0 was released on May 29, 2015.

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

Developments

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 vulnerabilities related to guessing social security numbers.

Technical details

• Octave is written in C++ using the C++ standard library.
• 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 versions 3.8.0 and later include a Graphical User Interface (GUI) in addition to the traditional Command Line Interface (CLI).

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. However, it does not support passing arguments by reference.

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 supports various data structures and allows object-oriented programming.

Its syntax is very similar to MATLAB, and careful programming of 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 changed, copied and used. The program runs on Microsoft Windows and most Unix and Unix-like operating systems, including OS X.

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. In this example, we see a structure "x" with elements "a", "b", and "c", (an integer, an array, and a string, respectively):

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 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());

C and C++ code can be integrated into GNU Octave by creating oct files, or using the Matlab compatible MEX files.

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.

In fact, Octave treats incompatibility with MATLAB as a bug; therefore, it can be considered a software clone, which doesn't infringe software copyright as per Lotus v. Borland court case.

Syntax compatibility

There are a few purposeful, albeit minor, syntax additions:

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 by cascaded indexing, e.g. [1:10](3);
4. Strings can be defined with the " character as well as the ' character;
5. When the variable type is single, Octave calculates the "mean" in the single-domain (Matlab in double-domain) which is faster but gives less accurate results;
6. Blocks can also be terminated with more specific Control structure keywords, i.e., endif, endfor, endwhile, etc.;
7. Functions can be defined within scripts and at the Octave prompt;
8. All operators perform automatic broadcasting or singleton expansion.
9. Presence of a do-until loop (similar to do-while in C).

Function compatibility

Many of the numerous MATLAB functions are available in GNU Octave, some of them are accessible through packages via Octave-forge, but not all of MATLAB functions are available in GNU Octave. List of unavailable functions exists in Octave, and developers are seeking for help to implement them. Looking for function __unimplemented.m__, leads to the list of unimplemented functions.

Unimplemented functions are also categorized in Image, Mapping, Optimization, Signal, and Statistics packages.

When an unimplemented function is called the following error message is shown:

  octave:1> quad2d
  warning: quad2d is not implemented. Consider using dblquad.
  
  Please read <http://www.octave.org/missing.html> to learn how you can
  contribute missing functionality.
  warning: called from
      __unimplemented__ at line 523 column 5
  error: 'quad2d' undefined near line 1 column 1

User interfaces

Until version 3.8, Octave did not come with a graphical user interface (GUI)/integrated development environment (IDE) by default. However, an official graphical interface based on Qt has now been migrated to the main source repository and is available with Octave 3.8, but not as the default interface. It has become the default interface with the release of Octave 4.0. Several 3rd-party graphical front-ends have been developed.

See also

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

External links

• Unofficial but recommended GNU Octave 3.8.2 builds for Windows

Documentation

• Online documentation.
• Octave wiki (Click twice – page redirects cause some browsers to time out).
• Reviewed entry in the Free Software Directory.
• Archived June 30, 2007 at the Wayback Machine
• Mailing List Archives on Nabble – Search all Octave mailing lists.
• Mailing List Archives on Gmane – Search all Octave mailing lists.

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 – Free software toolboxes for various problems from independent developers. Octave-forge packages provide functions designed to work with the Octave package system. 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 scientific computational modelling (e.g. 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 (PSOM: pipeline system for Octave and Matlab).
• 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
• FEATool – A fully integrated multiphysics finite element simulation toolbox with both GUI and command line support (including geometry and grid generation, solvers, and postprocessing).

Plotting tools

• PLplot – A replacement of the traditional gnuplot in GNU Octave, licensed under the GNU LGPL.
• Plotly – Interactive, browser-based, publication quality graphs. Can be shared and jointly edited.
• 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.").

MATLAB-like IDEs

• Xoctave (Windows, Linux and MAC; commercial) allows plugin and multi-language support.
• QtOctave (Windows, Linux; free under GPLv2+) Official development ceased June 2011.
• DomainMath IDE (Windows, Linux, Mac OS; GPLv3+), Last Update: Nov 30, 2013
• Octclipse (Linux; Eclipse Public LicenseGPLv3+) Eclipse based octave IDE. Last Update: 2012-12-11
• Octave UPM (in Spanish) Personalized version with integrated GUI

Other GUIs

• Cantor (Linux, Windows; GPLv2) A KDE mathematics application, with backends for R, Maxima, Octave, Scilab, Sage, KAlgebra, and Qalculate. Under active development as of 2011.
• OctaveNB (Linux, Windows, OS X; GPLv2) NetBeans IDE integration for GNU Octave. Last updated Apr 2009.
• Anoc Octave Editor (Android) A GUI for Android that uses a dedicated server to perform calculations and generate plots
• GNU TeXmacs supports Octave as backend

Web-based user interfaces (WUI)

• Online access to Octave – Allows you to perform simple Octave calculations online
• Octave online – use Octave within a web browser
• octave-online.net