# Changes

## FAQ

, 23:30, 22 October 2019
This is a list of frequently asked questions (FAQ) for GNU Octave users.
We are always looking for new questions (with answers), better answers, or both. Feel free to edit this page with your changes. If you have general questions about Octave, or need help for something that is not covered by the Octave manual or the FAQ, please use the help@octave.org mailing list.
This =Where do I get additional help?= If you can't find an answer to your question in this FAQ is intended to supplement, not replacewiki, or in the Octave [http://www.octave.org/doc/interpreter manual] ([http://www.octave.org/octave.pdf PDF]) you can: * Search for an answer in our [https://lists.gnu.org/archive/html/help-octave/ mailing list archives]* Contact our user community using our [https://lists.gnu. Before posting a question to the org/mailman/listinfo/help-octave help@octave.org mailing list, you should first check ] (feel free to subscribe to see if the topic is covered this mailing list)* Contact our user community using our [https://webchat.freenode.net/?channels=octave IRC chat room <code>#octave</code> in the manual.Freenode] <div class="tocinline">__TOC__</div>
=General=
==What is Octave?==
[https://www.gnu.org/software/octave/ GNU Octave ] is a high-level interactive interpreted language, primarily intended for numerical computations that . It provides capabilities for the numerical solution of linear and nonlinear problems, and for performing other numerical experiments. It also provides extensive graphics capabilities for data visualization and manipulation. GNU Octave is normally used through its interactive interface ([https://en.wikipedia.org/wiki/Command-line_interface CLI] and [https://en.wikipedia.org/wiki/Graphical_user_interface GUI]), but it can also be used to write non-interactive programs. The GNU Octave language is mostly compatible with quite similar to Matlabso that most programs are easily portable.1
The GNU Octave can do arithmetic for real, complex or integer-valued scalars and matrices, solve sets distribution includes a [http://www.octave.org/octave.pdf 1000+ page Texinfo manual]. Access to the complete text of nonlinear algebraic equations, integrate functions over finite and infinite intervals, and integrate systems of ordinary differential and differential-algebraic equationsthe manual is available via the <code>doc</code> command at the GNU Octave prompt.
==What is Octave uses the GNU readline library to handle reading and editing input. By default, the line editing commands are similar to the cursor movement commands used by GNU Emacs, and a vi-style line editing interface is also available. At the end of each session, the command history is saved, so that commands entered during previous sessions are not lost.Forge?==
The [https://octave.sourceforge.io/ Octave distribution includes Forge] is a 650+ page Texinfo manual. Access collection of [[packages]] for GNU Octave, something similar to the complete text of Matlab toolboxes. When talking about the manual is available via the doc command two projects at the same time, GNU Octave promptis usually referred to as Octave core (or just "core"). Octave Forge also serves as a test bed for code that may eventually end up in the core, and distributes binaries for systems with a lack of developers tools (mainly Windows).
==Who uses Octave?==
Lots of people. It seems that universities Universities use it for research and teaching, companies of all sizes, for development, and individualsfor whatever private purpose. This question comes often on Octave mailing lists, see See [[WhoUsesOctaveWho Uses Octave?]] for a few answers.
==Who develops Octave?==
Discussions about writing the software that would eventually become Octave started in about 1988 with James B. Rawlings and [http://jweaton.org/ John W. Eaton ] at the University of Texas. John W. Eaton was is the original author of Octave, starting full-time development in February 1992. He is still the primary maintainer. The community of users/and developers has in addition contributed some code and fuels the discussion on the mailing lists [https://lists.gnu.org/mailman/listinfo/help-octave help@octave.org ] (user forum), [https://lists.gnu.org/mailman/listinfo/octave-maintainers maintainers@octave.org ] (development issues), and octave-dev@lists.sourceforge.net (all things related to the Octave Forge repository of user-contributed functions).
==Why '''GNU''' "Octave"?==
The GNU Project Octave's name has nothing to do with music. It is named after [http://en.wikipedia.org/wiki/Octave_Levenspiel Octave Levenspiel], a former professor of John who was launched in 1984 famous for his ability to develop do quick back-of-the-envelope calculations. You can hear John pronounce the name "Octave" a complete Unix-like operating system which is free softwarefew times [http: //videolectures.net/mloss08_eaton_oct/ in this video]. We hope that GNU Octave will help perform computations with the GNU systemsame ease as Dr. Levenspiel.
==Why "GNU is a recursive acronym for “GNU's Not Unix”; it is pronounced guh-noo, approximately like canoe." Octave?==
The Free Software Foundation (FSF) [https://www.gnu.org/ GNU Project] was launched in 1984 to develop a complete Unix-like operating system which is free software: the principal organizational sponsor of the GNU Projectsystem. GNU is a recursive acronym for "GNU's Not Unix"; it is pronounced [https://www.gnu.org/gnu/pronunciation.en.html g'noo].
Octave became GNU Octave in 1997 (beginning with version 2.0.6). This meant agreeing to consider Octave a part of the GNU Project and support the efforts of the FSF. A big part of this effort is to adhere to the The [httphttps://www.gnufsf.org/prep/standards/standards.html GNU coding standards] and to benefit from GNU's infrastructure Free Software Foundation (e.g. [http://hg.savannah.gnu.org/hgweb/octave/ code hosting] and [http://bugs.octave.org bug tracking]FSF). Additionally, Octave receives [https://my.fsf.org/donate/working-together/octave sponsorship] from is the FSF's Working Together fund. However, Octave is not and has never been developed by principal organizational sponsor of the FSFGNU Project.
For more information about Octave became GNU Octave in 1997 (beginning with [[Release History|version 2.0.6]]). This meant agreeing to consider Octave a part of the GNU project, see httpProject and support the efforts of the FSF. A big part of this effort is to adhere to the [https://www.gnu.org/prep/standards/standards.html GNU coding standards] and to benefit from GNU's infrastructure (e.g. [https://hg.savannah.gnu.org/hgweb/octave/ code hosting] and [http://bugs.octave.org bug tracking]). Additionally, Octave receives [https://my.fsf.org/donate/working-together/octave sponsorship] from the FSF's Working Together fund. However, Octave is not and has never been developed by the FSF.
==What version should How can I usecite Octave?==
In general, Octave is free software and does not legally bind you will find the latest version on http://wwwto cite it.octave.org/download.html. It is recommended to use the stable version However, we have invested a lot of octave for general usetime and effort in creating GNU Octave, and the development version we would appreciate if you would cite if you want the latest features and are willing to tolerate instabilityused. To cite GNU Octave in publications use:
A list of user John W. Eaton, David Bateman, Søren Hauberg, Rik Wehbring ({{Release Year}}). GNU Octave version {{Release}} manual: a high-visible changes since the last release is available in the file NEWSlevel interactive language for numerical computations. The file ChangeLog in the source distribution contains a more detailed record of changes made since the last release URL https://www.gnu.org/software/octave/doc/v{{Release}}/
==On what platforms does Octave run?==A [https://en.wikipedia.org/wiki/BibTeX BibTeX] entry for [https://en.wikipedia.org/wiki/LaTeX LaTeX] users is:
@manual{, title = {{GNU Octave runs on various Unices—at least Linux and Solaris, Mac OS X} version {{Release}} manual: a high-level interactive language for numerical computations}, Windows and anything you can compile it on author = {John W. Binary distributions exist at least for Debian, SUSE, Fedora Eaton and RedHat Linuxes (Intel David Bateman and AMD CPUs, at least), for Mac OS X S{\o}ren Hauberg and Windows' 98Rik Wehbring}, 2000 year = <span>{</span>{{Release Year}}}, XP, Vista url = {https://www.gnu.org/software/octave/doc/v{{Release}}/}, and 7. }
Two and three dimensional plotting is fully supported using gnuplot and an experimental OpenGL backendRun {{manual|citation}} at the Octave prompt for details on how to best cite the Octave version you are running. Certain Octave packages also have recommended citations in which case use <code>citation package_name</code>.
The underlying numerical solvers Note that there are currently standard Fortran ones like LAPACK, LINPACK, ODEPACK, two reasons for citing the BLAS, etcsoftware used., packaged in a library of C++ classes One is giving recognition to the work done by others which we already addressed. If possible, the Fortran subroutines are compiled with The other is giving details on the system's Fortran compilerused so that experiments can be replicated. For this, you should cite the version of Octave and called directly from all packages used (you can get this information using the C++ functions<code>ver</code> command), as well as any details of your setup as part of your Methods. If that's not possible In addition, you can still compile Octave if should make your source available. See [http://software.ac.uk/so-exactly-what-software-did-you have the free Fortran -use How to C translator f2ccite and describe software] for more details and an in depth discussion.
==What documentation exists for Octave is also free software; you can redistribute it and/or modify it under the terms of the GNU General Public License, version 3, as published by the Free Software Foundation, or at your option any later version.?==
==How can I cite Besides this wiki, the GNU Octave?==distribution includes a [http://www.octave.org/doc/interpreter 1000+ page Texinfo manual] ([http://www.octave.org/octave.pdf PDF]). Access to the complete text of the manual is available via the {{manual|doc}} command at the GNU Octave prompt. If you have problems using this manual, or find that some topic is not adequately explained, indexed, or cross-referenced, please report it on http://bugs.octave.org.
Pointing to http://www.octave.org is good, because that gives people ==How can I report a direct way to find out more. If citation of a URL is not allowed by a publisher, or if you also want to point to a traditional reference, then you can cite the bug in Octave manual:?==
@BOOK{eatonPlease read our website http:2008, author = "John W//www.octave.org/bugs.html. Eaton, David Bateman, and Søren Hauberg", title = "GNU Octave Manual Version 3", publisher = "Network Theory Limited", year = "2008", isbn = "0-9546120-6-X" }
=Licensing issues=
==If I write code using Octave do I have to release it under the GPL?==
The answer depends on precisely how the code is written and how it works.:
* Code written '''entirely in the scripting language of Octave ''' (interpreted code in .m files) may be released under the terms of whatever license you choose.
* Code written using [https://www.gnu.org/software/octave/doc/interpreter/Oct_002dFiles.html Octave's native plug-in code interface ] (also known as a .oct file) necessarily links with Octave internals and is considered a derivative work of Octave and therefore . Therefore it must be released under terms that are compatible with the [https://www.gnu.org/licenses/gpl.html GPL].
* Code written using [https://www.gnu.org/software/octave/doc/interpreter/Mex_002dFiles.html Octave's implementation of the Matlab MEX interface ] may be released under the terms of whatever license you choose, provided that the following conditions are met:
:# The plugin should MEX file may not use any bindings that are specific to Octave. In other words, the MEX file must '''it has to use the MEX interface only'''. In other words, and not also call on other Octave internals. It it should be possible in principle to use the MEX file with other programs that implement the MEX interface (e.g., Matlab). For example including an Octave header file or calling an Octave function within the MEX file, that is not related with Octave's implementation of the MEX interface make the MEX file a derivative work of Octave and has therefore to be released under terms that are compatible with the [https://www.gnu.org/licenses/gpl.html GPL].:# The MEX file should may not be distributed together with Octave in such a way that they effectively create a single work. For example, you should not distribute the MEX file and Octave together in a single package such that Octave automatically loads and runs the MEX file when it starts up. There are other possible ways that you might to effectively create a single work; this is just one example.
A program * Code that '''embeds the Octave interpreter ''' (e.g., by calling the "<code>octave_main" </code> function), or that calls functions from Octave's libraries (e.g., liboctinterp, liboctave, or libcruft) is considered a derivative work of Octave and therefore must be released under terms that are compatible with the GPL.
==Since Will you change the MEX interface allows plugins to be distributed under terms that are incompatible with license of the GPL, does this mean that you are encouraging people to to write non-free software Octave libraries for Octaveme?==
'''No. The original reason for implementing the MEX interface for Octave was to allow Octave ''' Instead of asking us to run free software that uses MEX files (change the particular goal was to run SundialsTB in Octave). The intent was to liberate that software from Matlab and increase the amount of free software available to Octave users, not to enable people to write proprietary code licensing terms for Octave. For the good of the community, we strongly encourage users of Octave to recommend that you release the code they write for Octave your program under terms that are compatible with the GPL. This way the free software community can benefit from your work the same as you have benefited from the work of all the people who have contributed to Octave.
==Should I wrote a program that links with Octave libraries and I don't want favor the MEX interface to release it under the terms of avoid the GPL. Will you change the license of the Octave libraries for me?==
'''No. Instead ''' The original reason for implementing the [https://www.gnu.org/software/octave/doc/interpreter/Mex_002dFiles.html MEX interface] for Octave was to allow Octave to run free software that uses MEX files (the particular goal was to run [https://computation.llnl.gov/projects/sundials/release-history#sundialsTB sundialsTB] in Octave). The intent was to liberate that software from Matlab and increase the amount of asking us free software available to Octave users, not to enable people to change the licensing terms write proprietary code for Octave. For the good of the community, we recommend that you strongly encourage users of Octave to release your program the code they write for Octave under terms that are compatible with the [https://www.gnu.org/licenses/gpl.html GPL so that the free software community can benefit from your work the same as you have benefited from the work of all the people who have contributed to Octave].
=What=Why can's new t I use code from File Exchange in version series 3.4.N and 3.5.N of Octave?==
* ARPACK now distributed {{Quote|text=Content submitted to File Exchange may only be used with Octave* Indexing optimisations* FTP object using libcurl* Better consistency with ismatrix, issquare, and issymetric* Function handles aware of overloaded functions* More efficient matrix division by making MathWorks products. | |§ 2(a single LAPACK call* Other optimisations in matrix operations* bsxfun optimised for basic arithmetic functions* Matlab-style ignoring of output arguments using <tt>~<)(iii) [https://www.mathworks.com/matlabcentral/tt>* Many optimisations termsofuse.html Terms of the accumarray function* Sparse matrix indexing has been rewritten for speed* Configuration pseudo-variables like page_screen_output accept a "local" option argument to limit their scope to function scope* The pkg command now accepts a -forge option to pull packages directly from Octave-forge* Several dlmread improvements* Octave now uses gnulib for better cross-platform compatibilityUse]}}
Here are some features That does not apply to GNU Octave, therefore the usage is in general prohibited. It should suffice — although interpretations of this vary — to contact the author directly to send you the code personally (maybe released under a free license), or download the code from the author's own website, if available. [[Asking_for_package_to_be_released_under_GPL:_examples|Some examples of letters/email sent to authors for that have been around since 3.2purpose]].N
* integer types* fixed point arithmetic* sparse matrices* linear programming code based on GLPK* 64-bit compilation support* gzipped files and stream and consequently support of Matlab v7 files* better support for both msvc and mingw* a fully compatible MEX interface* many many other minor features and compatibility changes* an experimental OpenGL graphics toolkit to replace gnuplot* object orient programming* block comments* imwrite and imread (based on the GraphicsMagick library)* Lazy transpose <br/> Special treatment in the parser of things like "a' * b", where the transpose is never explicitly formed but a flag is rather passed to the underlying LAPACK code.* Single precision type* Improved array indexing <br/> The underlying code used for indexing of arrays has been completely rewritten and so the indexing of arrays is now significantly faster.=Installation=
Here are some older features that have been around since 2.1.N:==How can I install Octave on Windows?==
* NDArrays* cells:''See: [[Octave for Microsoft Windows]]''
The 3.5.N series is the current development release and will become a 3.6.N release in the future. This series brings the following new features:==How can I install Octave on macOS?==
* Perl compatible regular expressions* a profiler* broadcasting enabled :''See: [[Octave for all built-in binary elementwise operators=What documentation exists for Octave?=macOS]]''
Besides the current wiki, there are other important sources of documentation and help for ==How can I install Octave.on GNU/Linux?==
==What documentation exists :''See: [[Octave for Octave?==GNU/Linux]]''
The ==How can I install Octave distribution includes a 650+ page manual that on Android / what is also distributed under the terms of this Octave app in the GNU GPL. It is available on the web at http://www.octave.org/docs.html and you will also find there instructions on how to order a paper version.Google Play store?==
The complete text of the There is an '''unofficial''' Octave manual is also app available using the GNU Info system via the GNU Emacs, info, or xinfo programs, or by using the <tt>doc</tt> command to start the GNU info browser directly from for Android in the Google Play store. Please see [[Octave promptfor Android]] for more information.
If you have problems using this documentation, or find that some topic is not adequately explained, indexed, or cross-referenced, please report it ==How can I install Octave on http://bugs.octave.org.platform X?==
==Getting additional help==Octave currently runs on [[Octave for GNU/Linux|GNU/Linux]], [[Octave for macOS|macOS]], and [[Octave for Microsoft Windows|Windows]]. It should be possible to make Octave work on other systems as well. If you are interested in porting Octave to other systems, please contact the maintainers development mailing list [https://lists.gnu.org/mailman/listinfo/octave-maintainers maintainers@octave.org].
If you can't find an answer to your question, the help@octave.org mailing list is available for questions related to using, installing, and porting ==What Octave that are not adequately answered by the Octave manual or by this document.version should I use?==
==User community==For general use, it is recommended to use the latest stable version of Octave (currently {{Release}}), available from http://www.octave.org/download.html. For development and bleeding-edge features one can obtain the development source code from the Mercurial repository https://hg.savannah.gnu.org/hgweb/octave/graph/.
To subscribe to The used version of Octave is available via the {{manual|ver}} command and a list, go to http://www.octave.org/archive.html and follow of user-visible changes since the link to last release is available via the subscription page for {{manual|news}} command at the listGNU Octave prompt.
Please do not send requests to be added or removed from the mailing list, or other administrative trivia to the list itself.==On what platforms does Octave run?==
An archive of old postings Octave runs on any platform you can compile it on. Binary distributions exist for [[Octave for GNU/Linux|GNU/Linux]], [[Octave for macOS|macOS]], and [[Octave for Microsoft Windows|Windows]]. To work fully functional, Octave requires the used platform to support the help-octave mailing list is maintained on underlying numerical libraries like [https://en.wikipedia.org/wiki/Basic_Linear_Algebra_Subprograms BLAS], [https://en.wikipedia.org/wiki/LAPACK LAPACK], [http://www.octavesuitesparse.com SuiteSparse], etc., and for plotting [https://www.opengl.org/archiveOpenGL] or [http://www.gnuplot.htmlinfo/ gnuplot].
You will also find some user advice and ==How can I obtain Octave's source code spread over the web. Good starting points are the Octave Wiki http://wiki.octave.org and Octave-Forge http://octave.sourceforge.net?==
We also have [httpThe latest version of the Octave source code (and older versions) is available from://www.octave.org/chat.html an IRC chat room].
“I think I have found a bug in Since Octaveis distributed under the terms of the GPL, but I'm not sureyou can get Octave from a friend who has a copy. How do I know, and who should I tell?”
First, see the section [http://www.octave.org/bugs.html on bugs and bug reports in the ==How can I build Octave manual]. When you report a bug, make sure to describe the type of computer you are using, the version of the operating system it is running, and from the version of Octave that you are using. Also provide enough source code and configuration details of your operating system so that the Octave maintainers can duplicate your bug.?==
=How can I obtain To use Octave?=it is usually not required to build it from it's source code. Binary distributions exist for [[Octave for GNU/Linux|GNU/Linux]], [[Octave for macOS|macOS]], and [[Octave for Microsoft Windows|Windows]].
==Source If you have reasons to build Octave from the source code==, see [[Building]] for more information.
Source code is available on the ==What do I need to build Octave development site, where you are sure to get from the latest version.source code?==
Since Octave is distributed under the terms of the GPL, you can get ==Do I need GCC to build Octave from a friend who has a copy, or from the Octave website.source code?==
==PreNo. The development is done primarily with [https://gcc.gnu.org/ GCC], so you may hit some incompatibilities. Octave is intended to be portable to any standard conforming compiler (for example [https://clang.llvm.org/ clang] is know to work as well). If you have difficulties that you think are bugs, please report them to the [http://bugs.octave.org bug tracker], or ask for help on the [https://lists.gnu.org/mailman/listinfo/help-compiled binary packages==octave help@octave.org mailing list].
The =What's new in Octave project does not distribute binary packages, but other projects do. For an up-to-date listing of packagers, see:?=
* http://wwwEach new Octave release introduces many new features.octave.org A complete list of user visible changes can be seen by running <code>news</downloadcode> at the Octave prompt.html* [[Build From Source]] The following changes are a distilled list of the major changes:
As ==What's new in the next version of today, Octave binaries are available at least on Debian, Ubuntu, RedHat, Suse and Fedora GNU/Linuxen, Mac OS X, Windows' 98, 2000 and XP, Vista, and 7.?==
==How do I get a copy of Octave for (some other platform)?==See the [http://hg.savannah.gnu.org/hgweb/octave/file/tip/NEWS NEWS file] on the development branch.
Octave currently runs on Unix-like systems, Mac OS X, and Windows==What's new in version series 4. It should be possible to make Octave work on other systems as well0. If you are interested in porting X of Octave to other systems, please contact [mailto:maintainers@octave.org the maintainers' mailing list].==
=Installation issues and problems= See the complete user-visible changes on the [https://www.gnu.org/software/octave/NEWS-4.0.html NEWS file].
Octave 3* First official release of the GUI.4 requires approximately 1* Release of official windows binaries.3 GB of disk storage to unpack and compile from source (considerably less if you don't compile * Experimental support for [[classdef]].* OpenGL graphics with debugging symbols)Qt widgets. Once installed* Several functions for reading, writing, Octave requires approximately 355 MB and recording of disk space (again, considerably less if you don't compile with debugging symbols, approximately 50 MB)audio.
==What else do I need?'s new in version series 3.8.X of Octave==
To compile Octave, you will need a recent version of GNU MakeSee the complete user-visible changes on the [https://www. You will also need GCC 4gnu.org/software/octave/NEWS-3 or later, although GCC 4.4 or later is recommended8.html NEWS file].
'''You must have GNU Make to compile octave'''* Experimental GUI interface. * OpenGL graphics with fltk widgets.* Support for nested functions.* Support for java packages in Octave's Makefiles use features of GNU Make that are not present in other versions of makecore. GNU Make is very portable * Reading and easy to installwriting of image files vastly extended.
==Can I compile What's new in version series 3.6.X of Octave with another C++ compiler?==
Yes, but development is done primarily with GCC, so you may hit some incompatibilities. Octave is intended to be portable to any standard conforming compiler. If you have difficulties that you think are bugs, please report them to See the complete user-visible changes on the http[https://bugswww.octavegnu.org bug tracker, or ask for help on the [mailto:help@/software/octave/NEWS-3.org mailing list6.html NEWS file].
== Further links ==* Perl compatible regular expressions* Check the page [[Installation]] A profiler has been added.* Broadcasting enabled for more detailed information about installing Octaveall built-in binary element-wise operators.* Performance of all m-file string functions has been improved.
=Coding=What's new in version series 3.4.X of Octave==
==What features are unique to Octave?==See the complete user-visible changes on the [https://www.gnu.org/software/octave/NEWS-3.4.html NEWS file].
Although most * Many improvements to native OpenGL plotting* ARPACK now distributed with Octave* Indexing optimizations* FTP objects* Function handles aware of overloaded functions* bsxfun optimized for basic arithmetic functions* Matlab-style ignoring of output arguments using {{Codeline|~}}* Many optimizations of the accumarray function* Sparse matrix indexing has been rewritten for speed* The pkg command now accepts a -forge option to pull packages directly from Octave language will be familiar to Matlab users, it has some unique features of its own.Forge
==What's new in version series 3.2.X of Octave= Functions defined on the command-line===Functions can be defined by entering code on the command line, a feature not supported by Matlab. For example, you may type:
octaveSee the complete user-visible changes on the [https:1> function s = hello_string (to_who) > ## Say hello > if nargin<1, to_who = "World"; end > s = ["Hello ",\ > to_who]; > endfunction //www.gnu.org/software/octave:/NEWS-3.2> hello_string ("Moon") ans = Hello Moon.html NEWS file].
As a natural extension * Single precision type* Experimental OpenGL graphics toolkit to replace gnuplot* Object orient programming via @class named directories* 64-bit compilation support* gzipped files and stream and consequently support of this, functions can also be defined in script Matlab v7 files * a fully compatible MEX interface* imwrite and imread (m-files whose first non-comment line isn't <tt>function out = foo (...based on the GraphicsMagick library)</tt>) ===Comments with #=== The pound character, <tt>#</tt>, may be used to start comments, * Lazy transpose: Special treatment in addition to <tt>%</tt>. See the previous example. The major advantage parser of this is that as <tt>#</tt> is also a comment character for unix script files, any file that starts with a string things like <tt>#! /usr/bin/octave -q</tt> will be treated as an octave script and be executed by octave. ===Strings delimited by double quotes "=== The double quote, <tt>a' * b"</tt>, may be used to delimit strings, in addition where the transpose is never explicitly formed but a flag is rather passed to the single quote <tt>'</tt>underlying LAPACK code. See the previous example. Also, double-quoted strings include backslash interpretation (like C++, C, and Perl) while single quoted are uninterpreted (like Matlab and Perl). ===Line continuation by backslash===
Lines can be continued with a backslash, <tt>\</tt>, in addition to three points <tt>...</tt>. See the previous example. ===Informative block closing=Older releases==
You may close functionFor full details on older releases, for, while, if, ... blocks with endfunction, endfor, endwhile, ... keywords in addition to using end. As with Matlab, the end (or endfunction) keyword that marks the end of a function defined in a .m file is optional.see:
===Coherent syntax===* [http://hg.savannah.gnu.org/hgweb/octave/file/83792dd9bcc1/etc/NEWS.1 NEWS.1] for the 1.X.Y series* [http://hg.savannah.gnu.org/hgweb/octave/file/83792dd9bcc1/etc/NEWS.2 NEWS.2] for the 2.X.Y series* [http://hg.savannah.gnu.org/hgweb/octave/file/83792dd9bcc1/etc/NEWS.3 NEWS.3] for the 3.X.Y series
Indexing other things than variables is possible, as in:=Packages and Octave Forge=
octave:1> [3 1 4 1 5 9](3) ans = 4 octave:2> cos([0 pi pi/4 7])(3) ans = 0.70711How do I install or load all Octave Forge packages?==
In MatlabDo not do it! Really, it there is no reason to do this. Octave has many packages for example necessary to assign the intermediate result <tt>cos([0 pi pi/4 7])</tt> to different needs and is unlikely that you need all of them. You either have a variable before it can be indexed againsmall set of required packages, in which caseyou know them by name; or you want them all "just because", in which case you don't really need them.
===Exclamation mark as The common misconception is that the more packages one has installed and loaded, the more complete and powerful its Octave installation will be. However, in the same way one would never install all perl modules, ruby gems, python packages, and C++ libraries (because it simply makes no sense), one should not operator===install all Octave packages.
The exclamation mark <tt>!</tt> (aka “Bang!”) is a negation operatorPackages should be installed and loaded selectively. Note that some packages are meant to shadow core functions changing the way Octave works, just like and that different packages can have different functions with the tilde <tt>~</tt>:same name leading to unpredictable results.
If you really really really want to do load all packages, you can with the following:<syntaxhighlight lang="octave">## WARNING:1> if ! strcmp loading all packages is probably not the solution you are looking for.cellfun (@(x) pkg (program_name, "octaveload", x.name), > pkg ("It's an errorlist")); > else > "It works!" > end ans = It works!Note however that Matlab uses the <tt>!</ttsyntaxhighlight> operator for shell escapes, for which Octave requires using the system command.
===Increment and decrement operators=I have installed a package but still get a "foo undefined" error?==
If you like You have probably forgotten to load the <tt>++</tt>, <tt>+=</tt> etc operators, rejoice! Octave includes the Cpackage. Use {{Codeline|pkg load package-like increment and decrement operators <tt>++</tt> and <tt>--</tt> in both their prefix and postfix forms, in addition name}} to load it. Most packages are no longer loaded automatically to <tt>+=</tt>, <tt>-=</tt>, <tt>*=</tt>, <tt>/=</tt>, <tt>^=</tt>, <tt>avoid surprises. See reasoning on related FAQ [[FAQ#How_do_I_install_all_Octave_packages.*=</tt>, <tt>3F|how do I install all Octave packages]]./=</tt> If you want a specific package to be loaded by default at startup, and <tt>consider adding the {{Codeline|pkg load}} command on your {{path|[[.^=</tt>octaverc]]}} file.
For example, to pre-increment the variable x, you would write ++x==I cannot install a package. This would add one to x and then return the new value of x as the result of the expressionOctave complains about a missing mkoctfile. It is exactly the same as the expression x = x + 1.=
To post-increment a variable x, you would write x++. This adds one to the variable x, but returns the value that x had prior to incrementing itYou should normally use your distribution's packages. For exampleDebian and Fedora, if x is equal to 2, the result of the expression x++ is 2Octave package <code>foo</code> will be a deb or rpm called <code>octave-foo</code>, and the new value of x is 3you should install that instead using <code>apt</code> or <code>yum</code>.
For matrix and vector argumentsIf you really need to build Octave packages from source to install them, the increment and decrement operators work on each element you'll need {{manual|mkoctfile}}. Most distributions split Octave into several packages. The script {{manual|mkoctfile}} is then part of the operand.a separate package:
===Unwind* Debian/Ubuntu: [https://packages.debian.org/stretch/liboctave-protect===dev liboctave-dev]
In addition to try* Fedora: {{Codeline|octave-catch blocks, Octave supports an alternative form of exception handling modeled after the unwind-protect form of Lisp. The general form of an unwind_protect block looks like this:devel}}
unwind_protect body unwind_protect_cleanup cleanup end_unwind_protect==How do I automatically load a package at Octave startup?==
Where body and cleanup are both optional and may contain any When Octave expressions or commandsstarts, it runs the file {{Path|~/. The statements octaverc}} (in cleanup are guaranteed your user's home directory). If you want Octave to automatically load a package, simply add a <code>pkg load pkg-name</code> command to be executed regardless of how control exits bodyit. If the files does not exist, create it.
The unwind_protect statement is often used If you do this, remember that other people may not have Octave configured to reliably restore the values of global variables load packages at startup. Therefore, if you write code for others, remember that your programs still need to be temporarily changedload the packages they require.
Matlab can be made to do something similar with their <tt>OnCleanUp</tt> function that was introduced in 2008a. =Octave also has <tt>onCleanup</tt> since version 3.4.0.usage=
===Built-in ODE and DAE solvers=How do I execute an Octave script?==
Octave includes LSODE and DASSL for solving systems First of stiff ordinary differential all, make sure you understand [http://www.octave.org/doc/interpreter/Script-Files.html the difference between script files and differential-algebraic equationsfunction files]. These functions are built If you want to execute a function defined in to a file, just call the interpreter.function like any other Octave function: <code>foo(arg1, arg2);</code>
==How does To execute a script from within Octave solve linear systems?==, just type its name without the <code>.m</code> extension. Thus, if you have a script called <code>foo.m</code>, just type <code>foo</code> from within the Octave command prompt to execute it. You have to make sure that the script is in your current working directory or in Octave's load path. Type {{manual|pwd}} to get the current working directory or type {{manual|path}} to see which paths belong to Octave's load path. The current working directory is referred to as "." in the output of {{manual|path}}.
In addition If the script name has characters that are not valid for an Octave identifier, or if you do not want to use {{manual|addpath}} to consulting Octaveadd the script's source for location to the precise detailscurrent path, you can read use the Octave {{manual for a complete high-level description of the algorithm that Octave uses to decide how to solve a particular linear system, e.g. how the backslash operator <tt>A\x</tt> will be interpreted. Sections [http|run}} function instead://www.gnu.org/software/octave/doc/interpreter/Techniques-Used-for-Linear-Algebra.html#Techniques-Used-for-Linear-Algebra Techniques Used for Linear Algebra] and [http://www.gnu.org/software/octave/doc/interpreter/Sparse-Linear-Algebra.html Linear Algebra on Sparse Matrices] from the manual describe this procedure.
<syntaxhighlight lang=How do I"octave">run ("Script Name With Spaces.m")run ("/opt/local/foo..?=m")</syntaxhighlight>
==do xxxx?==An alternative is to run the script from outside Octave by calling Octave from your operating system shell. Unlike calling the script from inside Octave, this also allows you to pass arguments from the shell into the script, which the script can access using the {{manual|argv}} command:
You are probably looking for $octave the function ''lookfor''-script. This function searches the help text of all functions for a specific string and returns a list of functions. Note that by default it will only search the first line of the help text (check ''help lookfor'' at the octave prompt for more). The following example helps to find the function to calculate correlation coefficient in a matrix:m arg1 arg2 octaveIn a Unix environment, if the script has a [http:1> lookfor ("correlation") corr2 Returns the correlation coefficient between I and J//en. cor Compute correlationwikipedia. corrcoef Compute correlationorg/wiki/Shebang_%28Unix%29 shebang] (e. spearman Compute Spearman's rank correlation coefficient RHO for each of the variables sp autocor Return the autocorrelations from lag 0 to H of vector Xg.<code>#!/usr/bin/octave</code>) and executable permissions, you can call it like any other Unix program with arguments: Also, there's a high chance that$ ./the function name has a suggestive name, and so you can try auto-completion to get some hints. For the previous example, typing ''corr'' at the octave promp followed by pressing [Tab] twice would suggest the following:script arg1 arg2
octave:2> corr corr2 corrcoefIf you call the script from the shell and it's plotting, please note [[#When I try plotting from a script, why am I not seeing anything?|how to plot when running a script from the shell]].
==How do I erase close a figure?==
closeplot(); closefig(number)To close the current figure type {{manual|close}} in the Octave command prompt.
==How do I set the number of displayed decimals?==
octave:1> format long octave:2> pi pi = 3.14159265358979 octave:3> format short octave:4> pi pi = 3.1416 ==How do I vary the line thickness?== * There's plpot_octave, but the one in debian doesn't work for me.* Here's my octave hack for it--- http://gnufans.net/~deego/pub/octave/plot_width.m This one simply draws the line multiple times.* You can edit control the .eps file manually or number of displayed decimals using sed and awk.* Export the graph as fig file (gset term fig thickness 2). This also allows for easy postediting with xfig and export to formats not supported by gnuplot.* The gplot {{manual|format}} command of octave does not support gnuplot's linewidth parameter Thus you must use the graw() function for sending this option directly to gnuplot, eg. graw('replot "" notitle with lines lw 4\n');*Search the [http://octave.1599824.n4.nabble.com/ octave archives] for more. ==How do I call an octave function from C++?==
*Here is an untested code snippet for calling rand([9000,1]), modified from a post by HerberFarnsworth? to help-<syntaxhighlight lang="octave on 2003-05-01:">>> format long>> pipi = 3.14159265358979>> format short>> pipi = 3.1416</syntaxhighlight>
#include <octave/oct.h> ... ColumnVector NumRands(2); NumRands(0) = 9000; NumRands(1) = 1; octave_value_list f_arg, f_ret; f_arg(0) How do I call an Octave function from C++?= octave_value(NumRands); f_ret = feval("rand",f_arg,1); Matrix unis(f_ret(0).matrix_value());
==How do I create a full semilogPlease read the manual https:/log grid==/www.gnu.org/software/octave/doc/interpreter/Calling-Octave-Functions-from-Oct_002dFiles.html.
gset grid mxtics mytics gset grid lw 2, lw 0.1 grid("on");==How do I change color/line definition in gnuplot postscript?==
One can use postscript enhancement for proper axis gset format x "10^{%%L}"or gset format y "10^{%%L}"  ==How do I change colour/line definition in gnuplot postscript?==Here is a awk script to get a rainbow colour color map
#!/bin/awk -f
==How do I tell if a file exists?==
==How do I do X?==
==How do I create You are probably looking for the function {{manual|lookfor}}. This function searches the help text of all functions for a plot without specific string and returns a window popping up list of functions. Note that by default it will only search the first line of the help text (ie, a plot check <code>help lookfor</code> at the octave prompt for more). The following example helps to find the function to calculate correlation coefficient in a file)?==matrix:
figure(1, "visible", "off");>> lookfor correlation plot(sin(1:100));corr Compute matrix of correlation coefficients. corrcoef Compute a matrix of correlation coefficients. print -deps "/tmp/sinspearman Compute Spearman's rank correlation coefficient RHO.eps"
One Also, there's a high chance that the function name has a suggestive name, and so you can set that behaviour as defaulttry auto-completion to get some hints. For the previous example, typing <code>corr</code> at the octave prompt followed by pressing the {{key press|Tab}}-Key twice would suggest the following:
set(0, 'defaultfigurevisible', 'off');>> corr corr corrcoef
=Common problems=

==I do not see any output of my script until it has finished?==

By default Octave is set to pass its screen output through a [https://en.wikipedia.org/wiki/Terminal_pager pager] (usually the default pager is "less") which allows things such as navigating through the output with arrow keys or searching for text or regular expressions within the output. The pager only displays the output after it's finished receiving it, so when it is active you'll not be able to see anything until your script has terminated. To change this behavior temporarily or permanently you may want to use one of the options described [http://www.octave.org/doc/interpreter/Paging-Screen-Output.html in the manual].
==When I try plotting from a script, why am I not seeing anything?==
A common solution ==Why is to put a <tt>pause</tt> command at the end of your script.Octave's floating-point computation wrong?==
==How do I get sound output Floating-point arithmetic is an approximation '''in binary''' to arithmetic on real or complex numbers. Just like you cannot represent 1/3 exactly in Windows?== See http:decimal arithmetic (0.333333... is only a rough approximation to 1/3), you cannot represent some fractions like [itex]1/10</wwwmath> exactly in base 2.octave In binary, the representation to one tenth is [itex]0.org0\overline{0011}_b</octave-listsmath> where the bar indicates that it repeats infinitely (like how [itex]1/archive6 = 0.1\overline{6}_d</helpmath> in decimal). Because this infinite repetition cannot be represented exactly with a finite number of digits, rounding errors occur for values that appear to be exact in decimal but are in fact approximations in binary, such as for example how 0.3 -octave0.2003/msg015672 - 0.html for a start1 is not equal to zero.
==Why does Octave segfault when using "clear all;"?==In addition, some advanced operations are computed by approximation and are not guaranteed to be accurate, see [https://en.wikipedia.org/wiki/Rounding#Table-maker.27s_dilemma Table-maker's dilemma]. Their results are system-dependent.
This isn't an Octave bug. It happens with any program that uses [https://en.wikipedia.org/wiki/IEEE_754 IEEE 754 floating-point arithmetic]. To be fair, IEEE 754 also specifies decimal floating-point arithmetic, which has never seen wide adoption. The reason why Octave and other programs using IEEE 754 binary floating-point numbers is a known problem if that they are ''fast'', because they are implemented in hardware or system libraries. Unless you have one of the following packages loaded:are using very exotic hardware, Octave will use your computer's processor for basic floating-point arithmetic.
* ann* database* ftp Another approach to deal with rounding errors is interval arithmetic with the [[Interval package]] or symbolic computatons with the [[Symbolic package]]. These approaches are likely to be slower, since not all operations can be performed on Hardware like pure floatin-point arithmetic.
See To learn more about floating-point arithmetic, consult the [https://en.wikipedia.org/wiki/Floating-point_arithmetic Wikipedia article] or the classical reference by David Goldberg [http://wwwdocs.nabbleoracle.com/Segmentationcd/E19957-Fault01/806-3568/ncg_goldberg.html What Every Computer Scientist Should Know About Floating--Clear-all-td21998563Point Arithmetic].html for a discussion
==Octave takes a long time to find symbols.Missing lines when printing under Windows with OpenGL toolkit and Intel integrated GPU==
Octave uses the genpath function to recursively add directories to the list of directories searched for function files. Check the list of directories Some windows users with integrated Intel GPUs have reported missing lines when printing with the path command. If the path list is very long check your use of the genpath functionan OpenGL toolkit like FLTK or Qt.{{bug|42534}}
==When plotting Octave occasionally gives me errors like <tt>gnuplot> 9 0.735604 line 26317Users with this kind of problem should try to install/update their Intel OpenGL drivers for Windows or consider installing Mesa drivers from http: invalid command</tt>/qt-project.==There is a known bug in gnuplot 4.2 that can cause an off by one error while piping data to gnuplot. It has been fixed in gnuplot 4.4org/wiki/Cross-compiling-Mesa-for-Windows .
If you have obtained your copy of Octave from a distribution please file a bug report requesting that the fix reported in the above bug report be includedSee also https://www.opengl.org/wiki/FAQ#Why_is_my_GL_version_only_1.4_or_lower.3F .
==I cannot install a package. Octave complains about a missing mkoctfile.Plot hangs and makes the GUI unresponsive==
Most distributions split Octave into several packages. The script mkoctfile If the Qt graphics toolkit is used and "plot" is then part of used for the first time, the fontconfig scanner searches the font directory to build a separate package:font cache. This can take up to 3min on slow CPUs. See {{bug|45458}}
* Debian/Ubuntu<br/> <tt>aptitude install octave-headers</tt>==Error message about invalid call to script or invalid use of script in index expression==
* Fedora<brIf Octave shows an error message about {{Codeline|invalid call to script .../> <tt>yum install octaveclose.m}} or {{Codeline|invalid use of of script .../close.m in index expression}}, it means that you have created a script called close.m that is overriding the built-devel</tt>in Octave function {{Codeline|close}}. Octave functions and scripts share the samem global namespace. It is best to avoid creating your own scripts or functions that have the same name as an Octave function.
=Porting programs from Differences between Octave and Matlab to Octave=
<blockquote>
I wrote some code for Matlab, and I want to get it running under Octave. Is there anything I should watch out for?
</blockquote>
<blockquote>
I wrote some code in Octave, and want to share it with Matlab users. Is there anything I should watch out for?
</blockquote>
which is not quite the same thing. There are still a number of differences between Octave and Matlab, however in general differences between the two are considered as bugs. Octave might consider that the bug is in Matlab and do nothing about it, but generally functionality is almost identical. If you find a an important functional difference between Octave behavior and Matlab, then you should send a description of this difference (with code illustrating the difference, if possible) to http://bugs.octave.org.
Furthermore, Octave adds a few syntactical extensions to Matlab that might cause some issues when exchanging files between Matlab and Octave users. As both Octave and Matlab are under constant development the information in this section is subject to change at anytime.
You should also look at As both Octave and Matlab are under constant development, the page http://octave.sourceforge.net/packages.html and http://octave.sourceforge.net/doc/ that has a function reference that information in this section is up subject to date. You can use this function reference to see the number of octave function that are available and their Matlab compatibilitychange.
==How You should also look at the pages http://octave.sourceforge.net/packages.php and http://octave.sourceforge.net/docs.html that have a function reference that is Octave different from up to date. You can use this function reference to see the number of octave functions that are available and their Matlab?==compatibility.
The major differences between Octave 3.4.N and Matlab R2010b are:==Nested Functions==
===Nested Functions===Octave has limited support for nested functionssince version 3.8.0. That is
<syntaxhighlight lang="Matlab">function y = foo (x) y = bar(x) function y = bar (x) y = ...; end end</syntaxhighlight>
is equivalent to
<syntaxhighlight lang="Octave">function y = foo (x) y = bar(x) endendfunction  function y = bar (x) y = ...; endendfunction</syntaxhighlight>
The main difference with Matlab is a matter of scope. While nested functions have access to the parent function's scope in Matlab, no such thing is available in Octave, due to how Octave essentially “un-nests” nested functions.
The authors of Octave consider the nested function scoping rules of Matlab to be more problems than they are worth as they introduce difficult to find bugs as inadvertently modifying a variable in a nested function that is also used in the parent is particularly easyfor those not attentive to detail.
===Differences in core syntax===
There are a few core Matlab syntaxes that are not accepted by Octave, these being
* Some limitations on the use of function handles. The major difference is related to nested function scoping rules (as above) and their use with function handles.
* Some limitations of variable argument lists on the LHS of an expression, though the most common types are accepted.
* Matlab classdef object oriented programming is not yet only partially supported, though work is underway and when development more on to Octave 3.5 this will be included in the development treesee [[classdef]] for details.
===Differences in core functions===
A large number of the Matlab core functions (ie i.e. those that are in the core and not a toolbox) are implemented, and certainly all of the commonly used ones. There are a few functions that aren't implemented, usually to do with specific missing Octave functionality (GUI, DLL, Java, ActiveX, DDE, web, and serial functions). Some of the core functions have limitations that aren't in the Matlab version. For example the {{manual|sprandn }} function can not force a particular condition number for the matrix like Matlab can. Another example is that testing and the runtests function work differently in Matlab and Octave.
===Just-In-Time compiler===
Matlab includes a "Just-In-Time" compiler. This compiler allows the acceleration of for-loops in Matlab to almost native performance with certain restrictions. The JIT must know the return type of all functions called in the loops and so you can't include user functions in the loop of JIT optimized loops. Octave doesn't have has a [[JIT|not fully functional JIT and so to some might seem slower than Matlabcompiler]]. For this reason you must [[Performance#Vectorization|vectorize your code ]] as much as possible. The MathWorks themselves have a good document discussing vectorization at http://www.mathworks.com/support/tech-notes/1100/1109.html.
===Compiler===
On a related point, there is no Octave compiler, and so you can't convert your Octave code into a binary for additional speed or distribution. There have been several aborted attempts at creating an Octave compiler. Should the JIT compiler above ever be implemented, an Octave compiler should be more feasible.
===Graphic handles===
Up to Octave 2.9.9 there was no support for graphic handles in Octave itself. In the 3.2.N versions of Octave and beyond the The support for graphics handles is converging towards full compatibility. The patch function is currently limited to 2-D patches If you notice any incompatibilities, due to an underlying limitation in gnuplot, but the experimental OpenGL backend is starting to see an implementation of 3-D patchesplease [http://bugs.octave.org report a bug].
===GUI functions ===
There are no The support for [http://www.octave.org/doc/interpreter/GUI-Development.html Matlab compatible GUI functions yet] was added in Octave version 3.6.0 and is converging towards full compatibility. This might be an issue if If you intend to exchange Octave code with Matlab users. There are a number of bindings from Octave to Tcl/Tknotice any incompatibilities, VTK and Zenity included in the Octave Forge project (please [http://bugs.octave.sourceforge.net) for example that can be used for org report a GUI, but these are not Matlab compatible. Work on a Matlab compatible GUI is in an alpha stage in the QtHandles project, which may form part of a future release of Octavebug].
Octave itself includes no Simulink support. Typically the simulink models lag research and are less flexible, so shouldn't really be used in a research environment. However, some Matlab users that try to use Octave complain about this lack.
===MEX-Files===
Octave includes an [http://www.octave.org/doc/interpreter/Mex_002dFiles.html API to the Matlab MEX interface]. However, as MEX is an API to the internals of Matlab and the internals of Octave differ from Matlab, there is necessarily a manipulation of the data to convert from a MEX interface to the Octave equivalent. This is notable for all complex matrices, where Matlab stores complex arrays as real and imaginary parts, whereas Octave respects the C99/C++ standards of co-locating the real/imag parts in memory. Also due to the way Matlab allows access to the arrays passed through a pointer, the MEX interface might require copies of arrays (even non complex ones).
Block comments denoted by <ttcode>#{</ttcode> and <ttcode>#}</ttcode> markers (or <ttcode>%{</ttcode> and <ttcode>%}</ttcode>) are supported by Octave with some limitations. The major limitation is that block comments are not supported within [] or {}.
===Mat-File format===
There are some differences in the mat v5 file format accepted by Octave. Matlab recently introduced the "-V7.3" save option which is an HDF5 format which is particularly useful for 64-bit platforms where the standard Matlab format can not correctly save variables. Octave accepts HDF5 files, but is not yet compatible with the "-v7.3" versions produced by Matlab.
Although Octave can load inline function handles saved by Matlab, it can not yet save them.
Finally, Some some multi-byte Unicode characters aren't yet treated in mat-files.
===Profiler===
Current Octave releases don't have a profiler, but there is one in the 3.5 development version, thanks Thanks to Daniel Kraft's 2011 Google Summer of Code project, [http://www.octave.org/doc/interpreter/Profiling. It should be released with html Octave has a profiler] since version 3.6.0.
===Toolboxes===
Octave is a community project and so the toolboxes that exist are donated by those interested in them through the [[Octave Forge website (http://octave.sourceforge.net)]]. These might be lacking in certain functionality relative to the Matlab toolboxes, and might not exactly duplicate the Matlab functionality or interface.
===Short-circuit <ttcode>&</ttcode> and <ttcode>|</ttcode> operators===
The <ttcode>&</ttcode> and <ttcode>|</ttcode> operators in Matlab short-circuit when included in a condition (e.g. an {{Codeline|if }} or {{Codeline|while}} statement ) and not otherwise. In Octave only the <ttcode>&&</ttcode> and <ttcode>||</ttcode> short circuit. Note that this means that
<syntaxhighlight lang="Octave">if (a | b) ... end</syntaxhighlight>
and
<syntaxhighlight lang="Octave">t = a | b; if (t) ... end</syntaxhighlight> have different semantics in Matlab. This is really a Matlab bug, but there is too much code out there that relies on this behavior to change it. Prefer the <code>&&</code> and <code>||</code> operators in {{Codeline|if}} statements if possible.
have different semantics in Note that the difference with Matlab. This is really also significant when either argument is a Matlab bug, but there function with side effects or if the first argument is too much code out there that relies on this behaviour to change it. Prefer a scalar and the <tt>||</tt> and <tt>&&</tt> operators in <tt>if</tt> statements if possiblesecond argument is an empty matrix. If you need to use code written for Matlab that depends on this buggy behaviour For example, you can enable it since Octave 3.4.0 with note the following command:difference between
do_braindead_shortcircuit_evaluation<syntaxhighlight lang="Octave">t = 1 | []; ## results in [], so...if (t) 1, end ## in if ([]), this is false.</syntaxhighlight>
Note that the difference with Matlab is also significant when either argument is a function with side effects or if the first argument is a scalar and the second argument is an empty matrix. For example, note the difference between
t <syntaxhighlight lang= "Octave">if (1 | []; ## results in [], so... if (t) 1, end ## in if ([]), this short circuits so condition is falsetrue.</syntaxhighlight>
andIn the latter case, Octave displays since version 4.0.0 a warning:
if (1 | []) 1, end ## warning: Matlab-style short circuits so condition is true.-circuit operation performed for operator |
Another case that is documented in the Matlab manuals is that
<syntaxhighlight lang="Matlab">t = [1, 1] | [1, 2, 3]; ## error if ([1, 1] | [1, 2, 3]) 1, end ## OK</syntaxhighlight>
Also Matlab requires the operands of <ttcode>&&</ttcode> and <ttcode>||</ttcode> to be scalar values but Octave does not (it just applies the rule that for an operand to be considered true, every element of the object must be nonzero or logically true).
Finally, note the inconsistence of thinking of the condition of an <tt>{{Codeline|if</tt> }} statement as being equivalent to <tt>{{Codeline|all(X(:))</tt> }} when <tt>{{Codeline|X</tt> }} is a matrix. This is true for all cases EXCEPT empty matrices:
<syntaxhighlight lang="Matlab">if ([0, 1]) == if (all ([0, 1])) ==> i.e., condition is false. if ([1, 1]) == if (all ([1, 1])) ==> i.e., condition is true.</syntaxhighlight>
However,
<syntaxhighlight lang="Matlab">if ([])</syntaxhighlight>
is not the same as
<syntaxhighlight lang="Matlab">if (all ([]))</syntaxhighlight>
because, despite the name, the <tt>{{manual|all</tt> }} is really returning true if none of the elements of the matrix are zero, and since there are no elements, well, none of them are zero. This is an example of [httphttps://en.wikipedia.org/wiki/Vacuous_truth vacuous truth]. But, somewhere along the line, someone decided that <tt>{{Codeline|if ([])</tt> }} should be false. The Mathworks probably thought it just looks wrong to have <tt>{{Codeline|[]</tt> }} be true in this context even if you can use logical gymnastics to convince yourself that "all" the elements of an empty matrix are nonzero. Octave however duplicates this behavior for <tt>{{Codeline|if</tt> }} statements containing empty matrices.
===Solvers for singular, under- and over-determined matrices===
Matlab's solvers as used by the operators {{manual|mldivide (}} <code>\) </code> and {{manual|mrdivide (}} <code>/</)code>, use a different approach than Octave's in the case of singular, under-, or over-determined matrices. In the case of a singular matrix, Matlab returns the result given by the LU decomposition, even though the underlying solver has flagged the result as erroneous. Octave has made the choice of falling back to a minimum norm solution of matrices that have been flagged as singular which arguably is a better result for these cases.
In the case of under- or over-determined matrices, Octave continues to use a minimum norm solution, whereas Matlab uses an approach that is equivalent to
<syntaxhighlight lang="Octave">function x = mldivide (A, b) m = rows (A); [Q, R, E] = qr(A); x = [A \ b, E(:, 1:m) * (R(:, 1:m) \ (Q' * b))] end</syntaxhighlight>
While this approach is certainly faster and uses less memory than Octave's minimum norm approach, this approach seems to be inferior in other ways.
A numerical question arises: how big can the null space component become, relative to the minimum-norm solution? Can it be nicely bounded, or can it be arbitrarily big? Consider this example:
<syntaxhighlight lang="Octave">m = 10; n = 10000; A = ones(m, n) + 1e-6 * randn(m,n); b = ones(m, 1) + 1e-6 * randn(m,1); norm(A \ b)</syntaxhighlight>
while Octave's minimum-norm values are around about 3e-2, Matlab's results are 50-times larger. For another issue, try this code:
<syntaxhighlight lang="Octave">m = 5; n = 100; j = floor(m * rand(1, n)) + 1; b = ones(m, 1); A = zeros(m, n); A(sub2ind(size(A),j,1:n)) = 1; x = A \ b; [dummy~,p] = sort(rand(1,n)); y = A(:,p)\b; norm(x(p)-y)</syntaxhighlight>
It shows that unlike in Octave, {{manual|mldivide }} in Matlab is not invariant with respect to column permutations. If there are multiple columns of the same norm, permuting columns of the matrix gets you different result than permuting the solution vector. This will surprise many users.
Since the {{manual|mldivide (}} <code>\) </code> and {{manual|mrdivide (}} <code>/</) code> operators are often part of a more complex expression, where there is no room to react to warnings or flags, it should prefer intelligence (robustness) to speed, and so the Octave developers are firmly of the opinion that Octave's approach for singular, under- and over-determined matrices is a better choice than Matlab's.
===Octave extensions===
The extensions in Octave over Matlab MATLAB syntax are very useful, but might cause issues when sharing with Matlab users. A list of the major extensions that should be avoided to be compatible with Matlab are:
Comments in octave Octave can be marked with <tt>{{Codeline|#</tt>}}. This allows POSIX systems to have the first line as <tt>{{Codeline|#! octave -q</tt> }} and mark the script itself executable. Matlab MATLAB doesn't have this feature due to the absence of comments starting with <tt>{{Codeline|#</tt>}}".
Code blocks like if, for, while, etc can be terminated with block specific terminations like endif. Matlab MATLAB doesn't have this and all blocks must be terminated with end.
Octave has a lisp-like <tt>{{Codeline|unwind_protect</tt> }} block that allows blocks of code that terminate in an error to ensure that the variables that are touched are restored. You can do something similar with try/catch combined with <tt>{{Codeline|rethrow (lasterror ())</tt> }} in Matlab, however rethrow and lasterror are only available in Octave 2.9.10 and later. Matlab MATLAB 2008a also introduced <tt>{{Codeline|OnCleanUp</tt> }} that is similar to <tt>{{Codeline|unwind_protect</tt>}}, except that the object created by this function has to be explicitly cleared in order for the cleanup code to run.
Note that using try/catch combined with <tt>{{Codeline|rethrow (lasterror ())</tt> can not }} cannot guarantee that global variables will be correctly reset, as it won't catch user interrupts with Ctrl-C. For example
<syntaxhighlight lang="Matlab">global a a = 1; try _a = a; a = 2 while true end catch fprintf ('caught interrupt\n'); a = _a; rethrow (lasterror()); end</syntaxhighlight>
compared to
Typing Ctrl-C in the first case returns the user directly to the prompt, and the variable ''a'' is not reset to the saved value. In the second case the variable ''a'' is reset correctly. Therefore Matlab gives no safe way of temporarily changing global variables.=Development=
Indexing can ==When will feature X be applied to all objects in Octave and not just variables. Therefore <tt>sin(x)(1:10);</tt> for example is perfectly valid in Octave but not Matlab. To do the same in Matlab you must do <tt>y released or implemented?= sin(x); y = y([1:10]);</tt>
Octave has the operators <tt>++<When it's ready, sooner [http:/tt>, <tt>–</tt>, <tt>www.octave.org/get-=<involved.html if you help]. You can [https://savannah.gnu.org/tt>, <tt>+=<patch/tt>, <tt>*?group=</tt>, etcoctave send us patches] if you can implement feature X yourself. As Matlab doesn If you can't, if you are sharing code these should some [http://www.octave.org/commercial-support.html developers may be avoidedconvinced to work on your specific problem for some money].
Character strings ==How can I get involved in Octave can be denoted with double or single quotes. There is a subtle difference between the two in that escaped characters like <tt>\n</tt> (newline), <tt>\t</tt> (tab), etc are interpreted in double quoted strings but not single quoted strings. This difference is important on Windows platforms where the <tt>\</tt> character is used in path names, and so single quoted strings should be used in paths. Matlab doesn't have double quoted strings and so they should be avoided if the code will be transferred to a Matlab user.development?==
==GUI==This Be around. Be social. Participate in our mailing lists [https://lists.gnu.org/mailman/listinfo/help-octave help@octave.org] and [https://lists.gnu.org/mailman/listinfo/octave-maintainers maintainers@octave.org]. Find things about Octave you don't like, and start thinking about how to fix them. Many people who now contribute to Octave first spent several years helping in the mailing list before they started to delve into the code. A good way to learn Octave is to understand the problems other people are having with it, so being helpful in the mailing lists not only helps Octave as a small section whole, but it's probably one of the most frequent questionsalso prepares you to be a better Octave contributor.
===Is If you feel ready to dive right into the code, read the [[Developers]] wiki page or [http://www.octave.org/get-involved.html start here]. But do not send an email to the mailing lists listing your skills and offering to help. We won't just suggest things for you to do. We lack volunteers and we do need your help, but because of that, we also lack the time to provide good guidance and mentoring. If there is a GUI specific short-term project you would like to work on, say so, and just do it. Then ask for octave?===Nohelp or advice when you're doing it. It is a lot more important that you do something that you're actually interested on than something we suggested because it only matches your skills.
===Is there a GUI planned for We also need help with this wiki and the [http://www.octave?===Yes but it's still in development though. You can try org/doc/interpreter/ manual]. These are also important tasks. The documentation is easy to download patch, and the gui branch of octave and compile it yourselfhelp text for individual functions even more so. Seems to be stable enough Editing this wiki is even easier.
===How come there's still no GUI for Accurate bug reporting is also very useful. Find and report [http://bugs.octave?===The .org/ bugs], making an attempt to diagnose them. Eventually, you will also know how to fix them. If you want to help with bug reports or patches, subscribe to the [https://lists.gnu.org/mailman/listinfo/octave prompt is really really good-bug-tracker bug tracker mailing list]. Also You'll get updates on all bug activity, some people are of the opinion that a GUI actually slows down the learning of the languageand you can jump in when you seesomething you can help with.
AlsoLook at our [[projects]], octave is a community project. It has the functionalities [[short projects]], and [[Summer of Code Project Ideas]] if you need specific inspiration for coding tasks that its users are willing we would like to spend time working on. The fact there's no GUI for octave only shows that there's no enough interest on it (despite the ammount of times this question shows up)get done.
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