GNU Octave

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

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. Octave is rather a tool for scientific computation.

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 music (see Octave). 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

Octave language is interpreted.
It is simply structured programming as in C language.
Octave does not support argument passing by reference. Only pass-by-value is supported.
Octave programs exist as a group of functions called from a script.
The Octave language has support for many common C standard library constructs.
The Octave language can be extended to support UNIX system calls and functions.
The Octave language is matrix-based and provides various functions for matrix operation.
It does not have classes or objects, but it supports structures as in the C language.
The syntax is very similar to MATLAB, and careful programming will allow a script 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.

Features unique to Octave

Command and variable name completion

Typing a TAB character (ASCII code 9) 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 = 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, so it is no longer necessary to place an upper bound on the number of optional arguments that a function can accept.

Here is an example of a function that uses the new syntax to print a header followed by an unspecified number of values:

function foo (heading, ...)
  disp (heading);
  va_start ();
  while (--nargin)
    disp (va_arg ());
  endwhile
endfunction

Variable-length return lists

Octave also has a real mechanism for handling functions that return an unspecified number of values. For example:

function ^* = foo (n)
  for i = 1:n
    vr_val (i);
  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 like:

both use matrices as the fundamental data type.
Built-in support for complex numbers.
Powerful built-in math functions and extensive function libraries.
Extensibility in the form of user-defined functions.

The differences between Octave and MATLAB are usually because the authors of Octave decided on a better and subjective implementation than the way MATLAB does it, and so introduced "user preference variables" so as to customize Octave's behavior to be either MATLAB-compatible or to use Octave's new features.

External links

Octave.org Home Page
GNU Octave Reference Manual by John W. Eaton (ISBN 0954161726)
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.

Domain-specific programming languages | GNU project software | Numerical programming languages | Free mathematics software