GNU Octave

GNU Octave is a high-level programming language primarily intended for scientific computing and numerical computation. Octave helps in 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. Full development was started by John W. Eaton in 1992. The first alpha release dates back to 4 January 1993 and on 17 February 1994 version 1.0 was released. Version 7.1.0 was released on Apr 6, 2022.

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

Development history

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.

Acceleration with OpenCL or CUDA is also possible with use of GPUs.

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 has an OpenGL-based graphics engine to create plots, graphs and charts and to save or print them. Alternatively, gnuplot can be used for the same purpose.
* Octave includes a Graphical User Interface (GUI) in addition to the traditional Command Line Interface (CLI); see #User interfaces for details.

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 although function arguments are copy-on-write to avoid unnecessary duplication.

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 Linux, Android, and macOS.

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 with elements , , and , (an integer, an array, and a string, respectively):

octave:1> x.a = 1; x.b = , 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 =

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.
Octave also does augmented assignment, e.g. x += 5.

Unwind-protect

Octave supports a limited form of exception handling modelled after th
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 explicitly 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 + plus (varargin);
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 = 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( 0,1:

#include
...
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:

# Matrices as 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.

Octave treats incompatibility with MATLAB as a bug; therefore, it could be considered a software clone, which does not infringe software copyright as per ''Lotus v. Borland'' court case.

MATLAB scripts from the MathWorks' FileExchange repository in principle are compatible with Octave. However, while they are often provided and uploaded by users under an Octave compatible and proper open source BSD license, the FileExchange Terms of use prohibit any usage beside MathWorks' proprietary