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GNU Octave

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GNU Octave
Developer(s)John W. Eaton
Initial release1988
Repository
Written inC++
PlatformCross-platform
Available in19 languages
TypeScientific computing
LicenseGPL
Websitegnu.org/software/octave
Welcome screen of GNU Octave

GNU Octave is 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. As part of the GNU Project, it is free software under the terms of the GNU General Public License.

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. Levenspiel is known for his ability to perform quick back-of-the-envelope calculations.[1]

Deplopments

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.[2]

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, 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.[3] However, it does not support passing arguments by reference.[4]

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.[5]

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.[1] The program runs on Microsoft Windows and most Unix and Unix-like operating systems, including Mac OS X.[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. 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());

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,[8] therefore it can be considered a software clone, which doesn't infringe software copyright as per Lotus v. Borland court case.

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
  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.

See also

Further reading

  • Hansen, Jesper Schmidt (2011). GNU Octave. Beginner's Guide. Packt Publishing. ISBN 978-1-849-51332-6. {{cite book}}: Unknown parameter |month= ignored (help)
Wikibooks has a book on the topic of: Octave Programming Tutorial
Wikimedia Commons has media related to GNU Octave diagrams.

Documentation

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

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

Current versions of Octave do 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 will likely be released with Octave 4.0.[12][13] Several 3rd-party graphical front-ends have been developed:

MATLAB-like IDEs
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)

References

  1. ^ a b Eaton, John W. "About Octave". Retrieved 2009-06-28.
  2. ^ HPC, 8 July 2009.
  3. ^ "GNU Octave - Controlling subprocesses". 14 November 2008. Retrieved 2009-01-28.
  4. ^ "GNU Octave". Retrieved 2009-01-28.
  5. ^ "Summary of important user-visible changes for version 3.2". Retrieved 2012-01-05.
  6. ^ "FAQ: MATLAB compatibility". Retrieved 2009-04-04.
  7. ^ "FAQ: Getting Octave". Retrieved 2009-04-04.
  8. ^ [1]
  9. ^ "sv-lncs" (PDF). Retrieved 2013-07-07.
  10. ^ "Multi-level bootstrap analysis of stable clusters in resting-state fMRI" (PDF). Retrieved 2013-07-07.
  11. ^ [2][dead link]
  12. ^ "Octave-Maintainers list".
  13. ^ "Octave-Maintainers list".
  14. ^ "QtOctave End". - archived version :: translated archived version
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