# Changes

## FAQ

, 13 June
m
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 GNU Octave, or need help for something that is not covered by the Octave manual or the FAQ, please use the [https://mailman.cae.wisc.edu/listinfo/help-octave 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 GNU Octave manual ([httpshttp://www.gnuoctave.org/software/octave/doc/interpreter/ HTMLmanual], ([httpshttp://www.gnuoctave.org/software/octave/octave.pdf PDF])you can: * Search for an answer in our [https://lists. Before posting a question to the gnu.org/archive/html/help-octave/ mailing list archives]* Contact our user community using our [https://mailmanlists.caegnu.wisc.eduorg/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>
==What is Octave?==
[https://www.gnu.org/software/octave/ GNU Octave ] is a high-level interactive interpreted language, primarily intended for numerical computations. It provides capabilities for the numerical solution of linear and nonlinear problems, that 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.
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.
GNU ==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 GNU Octave distribution includes a 650+ page Texinfo manual. Access to the complete text of the manual is available via the doc command at the GNU Octave prompt. ==What is Octave-Forge?==[httphttps://octave.sourceforge.netio/ Octave-Forge] is a collection of [[packages ]] for GNU Octave, something similar to the Matlab toolboxes. When talking about the two projects at the same time, GNU Octave is usually referred to as Octave core (or just ''"core''"). [http://octave.sourceforge.net/ 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 [[Who 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).
==Why "Octave"?==
Octave's name has nothing to do with music. It's is named after [http://en.wikipedia.org/wiki/Octave_Levenspiel Octave Levenspiel], a former professor of John who was famous for his ability to do quick back-of-the-envelope calculations. You can hear John pronounce the name "Octave" a few times [http://videolectures.net/mloss08_eaton_oct/ in this video]. We hope that GNU Octave will help perform computations with the same ease as Dr. Levenspiel.
==Why <em>"GNU</em> " Octave?==
The [https://www.gnu.org/ GNU Project ] was launched in 1984 to develop a complete Unix-like operating system which is free software: the GNU system. GNU is a recursive acronym for "GNU's Not Unix"; it is pronounced [https://www.gnu.org/gnu/pronunciation.en.html g'noo].
The [https://www.fsf.org/ Free Software Foundation (FSF)] is the principal organizational sponsor of the GNU is a recursive acronym for “GNU's Not Unix”; it is pronounced guh-noo, approximately like canoeProject.
The Free Software Foundation Octave became GNU Octave in 1997 (FSFbeginning with [[Release History|version 2.0.6]]) is . This meant agreeing to consider Octave a part of the GNU Project and support the efforts of the principal organizational sponsor FSF. A big part of this effort is to adhere to the [https://www.gnu.org/prep/standards/standards.html GNU Projectcoding 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.
==How can I cite 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 [http://www.gnu.org/prep/standards/standards.html GNU coding standards] and to benefit from GNU's infrastructure (e.g. [http://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.?==
For more information about the Octave is free software and does not legally bind you to cite it. However, we have invested a lot of time and effort in creating GNU projectOctave, see httpand we would appreciate if you would cite if you used. To cite GNU Octave in publications use://www.gnu.org.
==What John W. Eaton, David Bateman, Søren Hauberg, Rik Wehbring ({{Release Year}}). GNU Octave version should I use?=={{Release}} manual: a high-level interactive language for numerical computations. URL https://www.gnu.org/software/octave/doc/v{{Release}}/
In general, you will find the latest version on httpA [https://wwwen.octavewikipedia.org/downloadwiki/BibTeX BibTeX] entry for [https://en.htmlwikipedia. It org/wiki/LaTeX LaTeX] users is recommended to use the stable version of octave for general use, and the development version if you want the latest features and are willing to tolerate instability.:
A list of user @manual{, title = {{GNU Octave} version {{Release}} manual: a high-visible changes since the last release is available in the file NEWSlevel interactive language for numerical computations}, author = {John W. The file ChangeLog in the source distribution contains a more detailed record of changes made since the last releaseEaton and David Bateman and S{\o}ren Hauberg and Rik Wehbring}, year = <span>{</span>{{Release Year}}}, url = {https://www.gnu.org/software/octave/doc/v{{Release}}/}, }
* Code written using [https://www.gnu.org/software/octave/doc/interpreter/Oct_002dFiles.html Octave's native code interface] (also known as a .oct file) necessarily links with Octave runs on various Unices—at least Linux internals and Solaris, Mac OS X, Windows and anything you can compile is considered a derivative work of Octave. Therefore it onmust be released under terms that are compatible with the [https://www. Binary distributions exist at least for Debian, SUSE, Fedora and RedHat Linuxes (Intel and AMD CPUs, at least), for Mac OS X and Windows' 98, 2000, XP, Vista, and 7gnu.org/licenses/gpl.html GPL].
Two and three dimensional plotting is fully supported * Code written using gnuplot and an experimental OpenGL backend[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 underlying numerical solvers MEX file may not use any bindings that are currently standard Fortran ones like LAPACK, LINPACK, ODEPACKspecific to Octave, '''it has to use the BLAS, etcMEX interface only'''. In other words, packaged it should be possible in a library of C++ classesprinciple to use the MEX file with other programs that implement the MEX interface (e.g. If possible, Matlab). For example including an Octave header file or calling an Octave function within the Fortran subroutines are compiled MEX file, that is not related with the systemOctave's Fortran compiler, implementation of the MEX interface make the MEX file a derivative work of Octave and called directly from has therefore to be released under terms that are compatible with the C++ functions[https://www.gnu.org/licenses/gpl. If html GPL].:# The MEX file may not be distributed together with Octave in such a way that's not possiblethey effectively create a single work. For example, you can still compile should not distribute the MEX file and Octave together in a single package such that Octave if you have automatically loads and runs the free Fortran MEX file when it starts up. There are other possible ways to C translator f2ceffectively create a single work; this is just one example.
* Code that '''embeds the Octave is also free software; you can redistribute it andinterpreter''' (e.g., by calling the <code>octave_main</code> function), or modify it under the terms of the GNU General Public Licensethat calls functions from Octave's libraries (e.g., version 3liboctinterp, as published by the Free Software Foundationliboctave, or at your option any later versionlibcruft) is considered a derivative work of Octave and therefore must be released under terms that are compatible with the GPL.
== How can I cite Will you change the license of the Octavelibraries for me? ==
'''No.''' Instead of asking us to change the licensing terms for Octave is , we recommend that you release your program under terms that are compatible with the GPL. This way the free software and does not legally bind community can benefit from your work the same as you to cite it. However,we have invested a lot benefited from the work of time and effort in creating GNU all the people who have contributed to Octave, and wewould appreciate if you would cite if you used.
Run {{codeline|citation}} at ==Should I favor the Octave prompt for details on how MEX interface to bestcite avoid the Octave version you are running. Certain Octave packages also haverecommended citations in which case use {{codeline|citation package_name}}.GPL?==
Ideally, you should cite '''No.''' 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 free software itselfavailable to Octave users, not a book or manualto enable people to write proprietary code for Octave. For the good of the community, like sowe strongly encourage users of Octave to release the code they write for Octave under terms that are compatible with the [https://www.gnu.org/licenses/gpl.html GPL].
@software{octave, author = {John W. Eaton and others}, title = {GNU Why can't I use code from File Exchange in Octave}, url ?= {http://www.octave.org}, version = {4.0.0}, date = {2015-05-27}, }
<blockquote>This work made use of the free software package GNU Octave, and the authors are grateful for the support of the Octave development community{{Quote|text=Content submitted to File Exchange may only be used with MathWorks products. | |§ 2(a)(iii) [https://www.mathworks.<com/matlabcentral/blockquote>termsofuse.html Terms of Use]}}
If a more traditional reference is requiredThat does not apply to GNU Octave, there therefore the usage is also 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 manual 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 eachOctave release that can be cited:purpose]].
@book{, author = {John W. Eaton, David Bateman, S\oren Hauberg, and Rik Wehbring}, title Installation= {{GNU Octave} version 4.0.0 manual: a high-level interactive language for numerical computations}, year = {2015}, url = {http://www.gnu.org/software/octave/doc/interpreter}, }
Note that there are two reasons for citing the software used. One is givingrecognition to the work done by others which we already addressed. The otheris giving details ==How can I install Octave on the system used so that experiments can be replicated.This is just as important, if not more.Windows?==
For this, you should cite the version of Octave and all packages used, aswell as any details of your setup as part of your Methods. In addition,you should make your source available. :''See: [http://software.ac.uk/so-exactly-what-software-did-you-use How to cite and describe software[Octave for Microsoft Windows]]for more details and an in depth discussion.''
==When will feature X be released or implementedHow can I install Octave on macOS?==When it's ready, sooner if you help. Send us patches if you can. We like patches. If you can't, some developers may be convinced to work on your specific problem for some money.
==How can I get involved in :''See: [[Octave development?==for macOS]]''
Be around. Be social. Participate in the [https://mailman.cae.wisc.edu==How can I install Octave on GNU/listinfo/help-octave help]and [https://mailman.cae.wisc.edu/listinfo/octave-maintainers maintainers]mailing lists. Find things about Octave you don't like, and start thinkingabout how to fix them. Many people who now contribute to Octave first spentseveral years helping in the mailing list before they started to delve intothe code. A good way to learn Octave is to understand the problems otherpeople are having with it, so being helpful in the mailing lists not onlyhelps Octave as a whole, but it also prepares you to be a better Octavecontributor.Linux?==
If you feel ready to dive right into the code, read :''See: [[Hacking | here]Octave for GNU/Linux]and [http://www.gnu.org/software/octave/get-involved.html here] forguidance. But do not send an email to the mailing lists listing yourskills 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 alsolack the time to provide good guidance and mentoring. If there is aspecific short-term project you would like to work on, say so, and justdo it. Then ask for help or advice when you're doing it. It is a lotmore important that you do something that you're actually interested onthan something we suggested because it only matches your skills.
We also need help with this wiki and the[http://www.gnu.org==How can I install Octave on Android /software/octave/doc/interpreter/ manual]. These arealso important tasks. The documentation what is easy to patch, and this Octave app in the help textfor individual functions even more so. Editing this wiki is even easier.Google Play store?==
Accurate bug reporting There is also very usefulan '''unofficial''' Octave app available for Android in the Google Play store. Find This Octave app is no longer freely available and reporthas become [httphttps://wwwen.gnuwikipedia.org/software/octavewiki/bugs.html bugsShareware#Nagware "nagware"], making an attempt todiagnose them. Eventually, you will also know how to fix them This is a sad turn of events. If you wantto help with bug reports or patches, subscribe to Please see [https://savannah.gnu.org/mail/?group=octave the bug tracker mailing list[Android]].You'll get updates on all bug activity, and you can jump in when you seesomething you can help withfor more information.
Look at our [[Projects]] and [[Summer of Code Project Ideas]] if you needspecific inspiration for coding tasks that we would like to get done. Seealso the list of [[short projects]].==How can I install Octave on platform X?==
=Licensing issues=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 I write code using What Octave do version should I have to release it under the GPLuse?==
The answer depends on precisely how 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 is written and how it worksfrom the Mercurial repository https://hg.savannah.gnu.org/hgweb/octave/graph/.
Code written entirely in the scripting language The used version of Octave (interpreted code in .m files) may be released under is available via the terms {{manual|ver}} command and a list of whatever license you chooseuser-visible changes since the last release is available via the {{manual|news}} command at the GNU Octave prompt.
Code written using ==On what platforms does Octave's native plug-in interface (also known as a .oct file) necessarily links with Octave internals and is considered a derivative work of Octave and therefore must be released under terms that are compatible with the GPL.run?==
Code written using Octave's implementation of 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 Matlab MEX interface may be released under used platform to support the terms of whatever license you chooseunderlying numerical libraries like [https://en.wikipedia.org/wiki/Basic_Linear_Algebra_Subprograms BLAS], [https://en.wikipedia.org/wiki/LAPACK LAPACK], [http://www.suitesparse.com SuiteSparse], etc., provided that the following conditions are metand for plotting [https://www.opengl.org/ OpenGL] or [http://www.gnuplot.info/ gnuplot].
# The plugin should not use any bindings that are specific to ==How can I obtain Octave. In other words, the MEX file must use the MEX interface only, and not also call on other Octave internals. It should be possible in principle to use the MEX file with other programs that implement the MEX interface (e.g., Matlab).# The MEX file should 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 effectively create a single work; this is just one example.'s source code?==
A program that embeds The latest version of the Octave interpreter source code (e.g., by calling the "octave_main" functionand older versions), or that calls functions is available 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 the MEX interface allows plugins to be distributed under terms that are incompatible with the GPL, does this mean that you are encouraging people to write non-free software for Octave?==* https://www.octave.org/download.html* https://ftp.gnu.org/gnu/octave/
No. The original reason for implementing the MEX interface for Since Octave was to allow Octave to run free software that uses MEX files (is distributed under the particular goal was to run SundialsTB in Octave). The intent was to liberate that software from Matlab and increase the amount terms of free software available to Octave users, not to enable people to write proprietary code for Octave. For the good of the communityGPL, we strongly encourage users of you can get Octave to release the code they write for Octave under terms that are compatible with the GPLfrom a friend who has a copy.
==How can I wrote a program that links with build Octave libraries and I don't want to release it under from the terms of the GPL. Will you change the license of the Octave libraries for mesource code?==
NoTo use Octave it is usually not required to build it from it's source code. Instead of asking us to change the licensing terms Binary distributions exist for [[Octave for GNU/Linux|GNU/Linux]], [[Octavefor macOS|macOS]], we recommend that you release your program under terms that are compatible with the 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 and [[Octavefor Microsoft Windows|Windows]].
==Why can't I use If you have reasons to build Octave from the source code from File Exchange in Octave? It's released under a BSD license!==, see [[Building]] for more information.
When one downloads code ==What do I need to build Octave from File Exchange and use it on non Mathworks software (such as Octave), they are violating the Matlab central [http://www.mathworks.co.uk/matlabcentral/termsofuse.html Terms of Use]. While the [http://en.wikipedia.org/wiki/BSD_licenses BSD licenses] does allow one to use such source code in Octave, it also allows others to further impose restrictions which Mathworks does through the MATLAB Central Terms of Use of their site:?==
{{quote|text=Content submitted to File Exchange may only be used with MathWorks products.|sign=Matlab central|source=For a list of build dependencies see [[http://www.mathworksBuilding]].co.uk/matlabcentral/termsofuse.html#content Terms of Use 2iii]}}
It should suffice -- although interpretations of this vary -- ==Do I need GCC to contact the author directly and have them send you the code personally, or download build Octave from the source code from the author's own website, if available.?==
No. 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 need have difficulties that code or you think that the code is usefulare bugs, please write the authors asking report them to release under a free license. Some examples of letters/email sent to authors can be found in the page [[Asking_for_package_to_be_released_under_GPLhttp:_examples|Asking //bugs.octave.org bug tracker], or ask for package to be released under GPLhelp on the [https: examples]//lists.gnu.org/mailman/listinfo/help-octave help@octave.org mailing list].
Feel free to remix and reuse, just make sure you use your name!=What's new in Octave?=
=What's Each new in Octave=release introduces many new features. A complete list of user visible changes can be seen by running <code>news</code> at the Octave prompt. The following changes are a distilled list of the major changes:
Each ==What's new Octave release introduces many new features. The following area distilled list of the major changes. A complete list of user visiblechanges can be seen by running {{codeline|news}} at in the Octave prompt, anda full list next version of changes is on the {{Filepath|Changelog}} distributed withthe Octave sources.?==
==Coming in a future release==See the [http://hg.savannah.gnu.org/hgweb/octave/file/tip/NEWS NEWS file] on the development branch].
==What's new in version series 4.0.X of Octave==
* Many improvements to native OpenGL plotting
* ARPACK now distributed with Octave
* Indexing optimisationsoptimizations
* FTP objects
* Function handles aware of overloaded functions
* bsxfun optimised optimized for basic arithmetic functions
* Matlab-style ignoring of output arguments using {{Codeline|~}}
* Many optimisations 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-forgeForge
==What's new in version series 3.2.X of Octave==
* a fully compatible MEX interface
* 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.
== Older releases ==
For full details on older releases, see:
* [http://hg.savannah.gnu.org/hgweb/octave/file/83792dd9bcc1/etc/NEWS.3 NEWS.3] for the 3.X.Y series
=What documentation exists for Packages and Octave?Forge=
Besides the current wiki, there are other important sources of documentation and help for ==How do I install or load all Octave.Forge packages?==
==What documentation exists Do not do it! Really, there is no reason to do this. Octave has many packages for Octave?==different needs and is unlikely that you need all of them. You either have a small 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.
The Octave distribution includes a 650+ page manual common misconception is that is also distributed under the terms of more packages one has installed and loaded, the GNU GPLmore complete and powerful its Octave installation will be. It is available on However, in the web at http://www.gnu.org/software/octave/doc/interpreter/ same way one would never install all perl modules, ruby gems, python packages, and you will also find there instructions on how to order a paper versionC++ libraries (because it simply makes no sense), one should not install all Octave packages.
The complete text of Packages should be installed and loaded selectively. Note that some packages are meant to shadow core functions changing the way Octave manual is also available using the GNU Info system via the GNU Emacs, info, or xinfo programsworks, or by using and that different packages can have different functions with the {{Codeline|doc}} command same name leading to start the GNU info browser directly from the Octave promptunpredictable results.
If you have problems using this documentationreally really really want to do load all packages, or find that some topic you can with the following:<syntaxhighlight lang="octave">## WARNING: loading all packages is probably not adequately explainedthe solution you are looking for.cellfun (@(x) pkg ("load", indexed, or cross-referencedx.name), please report it on http:pkg ("list"));<//bugs.octave.org.syntaxhighlight>
==Getting additional helpI have installed a package but still get a "foo undefined" error?==
==User communityI cannot install a package. Octave complains about a missing mkoctfile.==
To subscribe to the listYou should normally use your distribution's packages. For Debian and Fedora, go to http:Octave package <code>foo<//www.code> will be a deb or rpm called <code>octave.org-foo</archive.html code>, and follow the link to the subscription page for the listyou should install that instead using <code>apt</code> or <code>yum</code>.
Please do not send requests If you really need to be added or removed build Octave packages from the mailing listsource to install them, or other administrative trivia to the list itselfyou'll need {{manual|mkoctfile}}. Most distributions split Octave into several packages. The script {{manual|mkoctfile}} is then part of a separate package:
An archive of old postings to the help-octave mailing list is maintained on http* Debian/Ubuntu: [https://wwwpackages.octavedebian.org/archive.html.stretch/liboctave-dev liboctave-dev]
=Coding=How do I automatically load a package at Octave startup?==
==What features are unique When Octave starts, it runs the file {{Path|~/.octaverc}} (in 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 Octave?==it. If the files does not exist, create it.
Although most of the If you do this, remember that other people may not have Octave language will be familiar configured to Matlab usersload packages at startup. Therefore, it has some unique features of its ownif you write code for others, remember that your programs still need to load the packages they require.
==How do I execute an Octave script?==
First of all, make sure you understand [http://www.gnuoctave.org/software/octave/doc/interpreter/Script-Files.html the difference between script files and function files]. If you want to execute a function defined in a file, just call the function like any other Octave function: <code>foo(arg1, arg2);</code>
To execute a script from within Octave, 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 <code>path</code> in Octave to see what this path is, and type <code>{{manual|pwd</code> }} to print get the current working directory (where youor type {{manual|path}} to see which paths belong to Octave're currently standing)s load path. The current working directory is referred to as "." in the <code>output of {{manual|path</code>}}.
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 add the script's location to the current path, you can use the <code>{{manual|run</code> }} function instead:
<syntaxhighlight lang="octave"> run("Script Name With Spaces.m") octave> run("/opt/local/foo.m")</syntaxhighlight>
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 <code>{{manual|argv</code> }} command:
\$ octave the-script.m arg1 arg2
If 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 xxxxI close a figure?==
You are probably looking for To close the function ''lookfor''. 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 current figure type {{manual|close}} in the octave Octave command prompt for more). The following example helps to find the function to calculate correlation coefficient in a matrix:
octave> lookfor correlation corr2 Returns the correlation coefficient between ==How do I and J. cor Compute correlation. corrcoef Compute correlation. spearman Compute Spearman's rank correlation coefficient RHO for each of the variables sp autocor Return set the autocorrelations from lag 0 to H number of vector X. 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:displayed decimals?==
octave> corr corr2 corrcoefYou can control the number of displayed decimals using the {{manual|format}} command:
<syntaxhighlight lang="octave">>> format long>> pipi =How do I erase a figure?=3.14159265358979>> format short>> pipi = 3.1416</syntaxhighlight>
closeplot(); closefig(number)==How do I call an Octave function from C++?==
==How do I set Please read the number of displayed decimals?==manual https://www.gnu.org/software/octave/doc/interpreter/Calling-Octave-Functions-from-Oct_002dFiles.html.
octave:1> format long octave:2> pi pi = 3.14159265358979 octave:3> format short octave:4> pi pi = 3.1416How do I change color/line definition in gnuplot postscript?==
==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-octave on 2003-05-01:  #include <octave/oct.h> ... ColumnVector NumRands(2); NumRands(0) = 9000; 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()); ==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?==
Look at functions like One can use the function {{manual|exist}} to tell if a regular file, file_in_pathsay <code>foo.. and txt</code> exist in Octave's load path, or the other functions that their descriptions point to.  ==How do I create a plot without a window popping up (ie, a plot to a file)?==current directory:
'''This only works with gnuplot as graphics_toolkit<syntaxhighlight lang="octave">>> exist ("foo.txt", "file") # 2, if file exists, NOT with fltk. See [https:0 otherwiseans = 2<//savannah.gnu.org/bugs/?33180 Bug#33180]'''syntaxhighlight>
figure==How do I create a plot without a window popping up (1, "visible", "off"); plot(sin(1:100)to a file directly); print -deps "/tmp/sin.eps"?==
One can set that behaviour as default<syntaxhighlight lang="octave">figure (1, "visible", "off");plot (sin (1:100));print -deps "/tmp/sin.eps"</syntaxhighlight>
One can set(0, 'defaultfigurevisible', 'off');that behavior as default:
<syntaxhighlight lang== How do I make Octave use more precision? =="octave">set (0, "defaultfigurevisible", "off");</syntaxhighlight>
==How do I increase Octave's default numerical type is IEEE 754 doubles, a.k.a. hardware floats. This type has 52 bits of precision or about 16 decimal digits. It's implemented in your computer's hardware, in your CPU, so it's '''fast'''. This type is assumed throughout for Octave's calculations.?==
You can use Octave's default numerical type is [https://en.wikipedia.org/wiki/IEEE_754 IEEE 754] binary64 , a.k.a few other built-in types. The int64 "double" or "hardware floats". This type will have 63 has a precision of 53 bits of precisionor about 16 decimal digits. It is supported by each modern computer hardware, so it is really '''fast'''. One bit This type is used assumed throughout for the sign, but if you donOctave't want to lose that bits calculations. If more precision was required, uint64 one can be used instead. These obtain a "few bits more" by using integer types, howevere.g. {{manual|uint64}}, but in general one cannot represent numbers as large as the default double type, and can only represent integersexpect more precision from any '''fast''' numerical software. Furthermore, there is no way Just to represent integer literalsvisualize "how big" those numerical limits are, so if you do consider the following table:
{| class="wikitable"|+ Limits of some of Octave's data types obtained by {{manual|intmax}} and {{manual|flintmax}}.|-| <code>intmax ("uint64")</code>| style="text-align: right;" | <code>18,446,744,073,709,551,615</code>| <code>2^64-1</code>|-| <code>intmax ("int64")</code>| style="text-align: right;" | <code>9,223,372,036,854,775,807</code>| <code>2^63-1</code>|-| <code>flintmax ("double")<syntaxhighlight lang/code>| style="Octavetext-align: right;"| <code>9,007,199,254,740,992</code>| <code>2^53</code>uint64|-| <code>flintmax (18446744073709551610"single")</code>| style="text-align: right;" | <code>16,777,216</code>| <code>2^24</syntaxhighlightcode>|}
the literal When working with other types than "18446744073709551610double" first gets converted in Octave, one has to a double precision typemake sure, so <code>uint64</code>'s additional precision that the first operand is lost. Instead, initialise the <code>uint64</code> with smaller numbers and perform a computation converted to get the larger number you want. E.g., desired type:
<syntaxhighlight lang="Octave">>>uint64(9999999999999992^53 + 1) * 10000ans = 9007199254740992>> uint64 (2^53) + 1ans = 9007199254740993</syntaxhighlight>
would produce value 9999999999999990000Notice the difference, which in the first line the addition within the brackets is close performed using double precision, therefore the result gets "truncated" to the maximum possible value for the without a warning. The third line uses throughout uint64 type, but can't be at the moment input directly, doing uint64(9999999999999990000), due to the mentioned error of roundingprecision.
Alternatively, one may use arbitrary Consider carefully if your problem really needs more precision arithmetic, which has as much . Often if you're running out of precision as is practical to hold the problem lies fundamentally in your computer's memorymethods being [https://en. The ''symbolic'' package has a vpa() function for arbitrary precision arithmeticwikipedia. Note that arbitrary org/wiki/Numerical_stability numerically unstable], thus more precision arithmetic must be implemented '''in software''' which makes it much slower than hardware floatswill not help you here.
Consider carefully if your problem really needs If you absolutely must have more precision. Often if , you're running out of precision the problem lies fundamentally in your methods being at present better off using a [httphttps://en.wikipedia.org/wiki/Numerical_stability numerically unstableComputer_algebra_system CAS]instead of Octave. However, so more precision will not help you here. If you absolutely CAS or symbolic computations must use arbitrary-precision arithmetic, yoube implemented '''in software'''re at present better off using a CAS instead of Octavewhich makes it much slower than hardware floats. An example of such a CAS is [http://www.sagemath.org / Sage] or have a look at Octave's [[Symbolic package]].
==How do I run a Matlab P-file in Octave?==
You can't. Matlab P-files (files with a <code>.p </code> file extension), also known as P-code, are [https://en.wikipedia.org/wiki/Obfuscation_%28software%29 obfuscated] files than cannot be run outside of Matlab itself. The original source Matlab m-files that were used to generate the these P-files should be used in Octave instead.
There are no plans to support running P-files produced by Matlab in Octave.
=Common problems=How does Octave solve linear systems?==
==I am running In addition to consulting Octave's source for the precise details, you can read the Octave manual for a script complete high-level description of the algorithm that should produce output during execution but I don't see anything until it has finished==Octave uses to decide how to solve a particular linear system, e.g. how the backslash operator <code>A \ x</code> will be interpreted. Sections [http://www.octave.org/doc/interpreter/Techniques-Used-for-Linear-Algebra.html Techniques Used for Linear Algebra] and [http://www.octave.org/doc/interpreter/Sparse-Linear-Algebra.html Linear Algebra on Sparse Matrices] from the manual describe this procedure.
By default Octave is set to pass its screen output through a pager (usually the default pager is "less") which allowsthings 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.gnu.org/software/octave/doc/interpreter/Paging-Screen-Output.html here].==How do I do X?==
==When I try plotting from You are probably looking for the function {{manual|lookfor}}. This function searches the help text of all functions for a script, why am I not seeing anything?==specific string and returns a list of functions. Note that by default it will only search the first line of the help text (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 matrix:
If you are running an Octave script that includes >> lookfor correlation corr Compute matrix of correlation coefficients. corrcoef Compute a plotting command, the script and Octave may terminate immediatelymatrix of correlation coefficients. So the plot window does show up, but immediately closes when Octave finishes execution. Alternatively, if using fltk, the plot window needs a readline loop to show up (the time when Octave is sitting around doing nothing waiting for interactive input) spearman Compute Spearman's rank correlation coefficient RHO.
A common solution is Also, there's a high chance that the function name has a suggestive name, and so you can try auto-completion to put a get some hints. For the previous example, typing <code>corr</code> at the octave prompt followed by pressing the {{Codelinekey press|pauseTab}} command at -Key twice would suggest the end of your script.following:
==How do I get sound input or output in Windows?== >> corrSound input from a sound card and output to a sound card is fully supported in Octave 4.0.0 and newer in all operating systems. Older versions of Octave had very limited audio support that was essentially Linux-specific. If you have problems with the audio I/O functions using Octave 4.0 or a newer version, please report them on the [http://bugs.octave.org bug tracker]. corr corrcoef
==I cannot install a package. Octave complains about a missing mkoctfile.=Common problems=
You should normally use your distribution's packages. For Debian and Fedora, Octave package '''foo''' will be a deb or rpm called '''octave-foo''', and you should install that instead using apt or yum.==I do not see any output of my script until it has finished?==
If you really need to build By default Octave packages from source is set to install thempass 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 need mkoctfilenot be able to see anything until your script has terminated. Most distributions split Octave into several packages. The script mkoctfile is then part To change this behavior temporarily or permanently you may want to use one of a separate packagethe options described [http://www.octave.org/doc/interpreter/Paging-Screen-Output.html in the manual].
* Debian/Ubuntu: {{Codeline|octave-headers}} or {{Codeline|liboctave-dev}}==When I try plotting from a script, why am I not seeing anything?==
* Fedora: {{Codeline|octave-devel}}If you are running an Octave script that includes a plotting command, the script and Octave may terminate immediately. So the plot window does show up, but immediately closes when Octave finishes execution. Alternatively, if using fltk, the plot window needs a readline loop to show up (the time when Octave is sitting around doing nothing waiting for interactive input).
== I'm having problem XXX using A common solution is to put a {{manual|pause}} command at the latest Octave version ==end of your script.
Please be more specific. What is the latest version, according to you? If you mean the latest released version, be aware that you may still have an older version due to whatever distribution method you're using. There may be a newer version available that you're not aware of due to the distribution method you're using to ==How do I get Octave, and sound input or output in most cases, there is a way to get a newer version via your distribution method (see other wiki pages for [[Octave_for_GNU/Linux|GNU/Linux]], [[Octave_for_MacOS_X|Mac OSX]], and [[Octave_for_Windows|Windows]]).?==
Sound input from a sound card and output to a sound card is fully supported since Octave 4.0.0 for all platforms. If you mean have problems with the latest Mercurial revision[http://www.octave.org/doc/interpreter/Audio-Processing.html audio I/O functions] using Octave 4.0.0 or a newer version, please specify which one that is. "Latest tip" is not informative, because from the time you wrote "latest tip" to report them on the time someone reads that message, "latest tip" might have changed meaning[http://bugs. Also, you might be standing on a different commit than what "hg tip" saysoctave. The tip may be on a different branch, or you might have updated to a different revision different from what "hg tip" saysorg bug tracker].
Instead, report ==I have problem X using the output of "hg summary" or "hg id". Also please use hashes instead or in addition to revision numbers. Revision numbers are just a convenience and only make sense in your local repo, and might not coincide with what someone sees on their own repo. Hashes are globally unique across all repos.latest Octave version==
If your problem truly persists with the latest version, as indicated [http://www.gnu.org/software/octave/download.html here], then by all means report a bug or ask for help, but don't Please be surprised if volunteers are less inclined to help more specific about what you with a problem that only exists in an older mean by "latest version of Octave."?
== Why * The latest stable version is this floating point computation wrong? =={{Release}}. Be aware that you may still have an older version due to whatever distribution method you are using. To get a newer stable version for your system see for example [[Octave for GNU/Linux|GNU/Linux]], [[Octave for macOS|macOS]], or [[Octave for Microsoft Windows|Windows]]).
Floating point arithmetic is an approximation '''in binary''' to arithmetic on real or complex numbers. Just like * If you cannot represent 1/3 exactly in decimal arithmetic (0.333333 is only a rough approximation refer to 1/3)the latest Mercurial revision, you cannot represent some fractions like $1please specify the [https:/10</math> exactly in base 2www.mercurial-scm. In binaryorg/wiki/ChangeSetID changeset ID] not the revision number, e.g. the representation to one tenth is output of <mathcode>0.0\overline{0011}_bhg summary</mathcode> where the bar indicates that it repeats infinitely (like how or <mathcode>1/6 = 0.1\overline{6}_dhg id</mathcode> 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 Changeset IDs are in fact approximations in binary, such as for example how 0.3 - 0.2 - 0.1 is not equal to zeroglobally unique across all repos. In additionIf your problem truly persists with the "latest version", some advanced operations are computed by approximation and are not guaranteed to be accurate, see then please [http://bugs.octave.org/ report a bug] or ask for help at[https://enlists.wikipediagnu.org/wikimailman/listinfo/Rounding#Tablehelp-makeroctave help@octave.27s_dilemma Table-maker's dilemmaorg]. Their results Otherwise, don't be surprised if volunteers are system-dependentless inclined to help you with a problem that only exists in an older version of Octave and is already fixed in a newer version. This isn't an Octave bug. It happens with any program that uses [http://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 use IEEE 754 binary floats ==Why is that they are ''fast'', because they are implemented in hardware or system libraries. Unless you are using very exotic hardware, Octave will use your computer's processor for basic floating -point arithmetic.computation wrong?== Like death and taxes, rounding errors are a fact of lifeFloating-point arithmetic is an approximation '''in binary''' to arithmetic on real or complex numbers. You Just like you cannot avoid themrepresent 1/3 exactly in decimal arithmetic (0.333333.. You can . is only move a rounding error from one part of a computation rough approximation to another1/3), or you can use more precision and delay the rounding errorcannot represent some fractions like [itex]1/10$ exactly in base 2. One way to delay In binary, the rounding error is representation to use arbitrary precision arithmetic, which one tenth is inevitably slower as $0.0\overline{0011}_b$ where the bar indicates that it has repeats infinitely (like how $1/6 = 0.1\overline{6}_d$ 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 implemented exact in software instead of hardwaredecimal but are in fact approximations in binary, such as for example how 0.3 - 0.2 - 0. You may use the vpa function from the symbolic package for this purpose1 is not equal to zero.
Another approach In addition, some advanced operations are computed by approximation and are not guaranteed to the problem is interval arithmetic with the be accurate, see [[Interval packagehttps://en.wikipedia.org/wiki/Rounding#Table-maker.27s_dilemma Table-maker's dilemma]]. Then, the exact result would always be enclosed by two binary floats. Again, this is slower since only the most basic interval arithmetic operations can be performed in hardware Their results are system-dependent.
To learn more about floating point arithmetic, consult This isn't an Octave bug. It happens with any program that uses [httphttps://en.wikipedia.org/wiki/Floating_point_arithmetic its Wikipedia articleIEEE_754 IEEE 754 floating-point arithmetic] or the classical reference [http://. To be fair, IEEE 754 also specifies decimal floating-pointarithmetic, which has never seen wide adoption. The reason why Octave and other programs using IEEE 754 binary floating-guipoint numbers is that they are ''fast'', because they are implemented in hardware or system libraries.de/ What Every Computer Scientist Should Know About Floating Point Arithmetic] Unless you are using very exotic hardware, Octave will use your computer's processor for basic floating-point arithmetic.
== I have installed a Another approach to deal with rounding errors is interval arithmetic with the [[Interval package but still get a "foo undefined" error ==]] 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.
== Missing lines when printing under Windows with OpenGL toolkit and Intel integrated GPU ==
Some windows users with integrated Intel GPUs have reported missing lines when printing with an OpenGL toolkit like FLTK or Qt. {{bug|42534}}
Users with this kind of problem should try to install/update their Intel OpenGL drivers for Windows or consider installing Mesa drivers from http://qt-project.org/wiki/Cross-compiling-Mesa-for-Windows.
== Plot hangs and makes the GUI unresponsive ==
If the Qt graphics toolkit is used and "plot" is used for the first time, the fontconfig scanner searches the font directory to build a font cache. This can take up to 3min on slow CPUs. See {{bug|45458}}
==Error message about invalid call to script or invalid use of script in index expression== If Octave shows an error message about {{Codeline|invalid call to script .../close.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-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. = Differences between Octave and Matlab =
<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 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.
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 up to date. You can use this function reference to see the number of octave functions that are available and their Matlab compatibility.
== 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 easy for 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 in a branch of 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 {{Forge|tcl-octave|Tcl/Tk}}notice any incompatibilities, please [http://octavizbugs.sourceforgeoctave.net/index.php? VTKorg report a bug] and {{Forge|zenity}} for example, that can be used for 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 Octave.
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 {{Codeline|<code>#{}} </code> and {{Codeline|<code>#&#125;}} </code> markers (or {{Codeline| <code>%{}} </code> and {{Codeline|<code>%&#125;}}</code>) 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 multi-byte Unicode characters aren't yet treated in mat-files.
== Profiler ==
Thanks to Daniel Kraft's 2011 Google Summer of Code project, [http://www.octave.org/doc/interpreter/Profiling.html Octave has a profiler ] since version 3.6.0. However, at the moment it only produces text output and has its own makeshift interface for hierarchical profiling.
== Toolboxes ==
Octave is a community project and so the toolboxes that exist are donated by those interested in them through [[Octave Forge]]. These might be lacking in certain functionality relative to the Matlab toolboxes, and might not exactly duplicate the Matlab functionality or interface.
== Short-circuit {{Codeline|<code>&}} </code> and {{Codeline<code>|&#124;}} </code> operators ==
The {{Codeline|<code>&}} </code> and {{Codeline<code>|&#124;}} </code> 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 {{Codeline|<code>&&}} </code> and {{Codeline<code>||&#124;&#124;}} </code> 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 {{Codeline|&#124;&#124;}} and {{Codeline|&&}} operators in {{Codeline|if}} 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 {{Codeline|<code>&&}} </code> and {{Codeline<code>||&#124;&#124;}} </code> 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 {{Codeline|if}} statement as being equivalent to {{Codeline|all(X(:))}} when {{Codeline|X}} 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 {{Codelinemanual|all}} 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 {{Codeline|if ([])}} should be false. The Mathworks probably thought it just looks wrong to have {{Codeline|[]}} 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 {{Codeline|if}} 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 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:
Octave has a lisp-like {{Codeline|unwind_protect}} 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 {{Codeline|rethrow (lasterror ())}} in Matlab, however rethrow and lasterror are only available in Octave 2.9.10 and later. MATLAB 2008a also introduced {{Codeline|OnCleanUp}} that is similar to {{Codeline|unwind_protect}}, 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 {{Codeline|rethrow (lasterror ())}} 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
<syntaxhighlight lang="Octave">global a a = 1; unwind_protect _a = a; a = 2 while true end unwind_protect_cleanup fprintf ('caught interrupt\n'); a = _a; end</syntaxhighlight>
Typing Ctrl-C in the first case returns the user directly to the prompt, and the variable ''<code>a'' </code> is not reset to the saved value. In the second case the variable ''<code>a'' </code> is reset correctly. Therefore Matlab gives no safe way of temporarily changing global variables.
Indexing can be applied to all objects in Octave and not just variables. Therefore {{Codeline|sin(x)(1:10)}} for example is perfectly valid in Octave but not Matlab. To do the same in Matlab you must do {{Codeline|y &#61; sin(x); y &#61; y([1:10]);}}
Character strings in Octave can be denoted with double or single quotes. There is a subtle difference between the two in that escaped characters like {{Codeline|\n}} (newline), {{Codeline|\t}} (tab), etc are interpreted in double quoted strings but not single quoted strings. This difference is important on Windows platforms where the {{Codeline|\}} 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.
==Does Octave have a GUI?==
'''Yes! ''' It was officially released with Octave 4.0.0. It wasalso available since version 3.8.0 has as an experimental feature (use the{{Codeline|--force-gui}} option to start Octave).
==Why did you create yet another GUI instead of making one that already exists better?==
None of the GUIs for Octave that had been developed thus far were part of
Octave and there is a reason for it. All of them failed at a very important
point, integration with Octave. They treated Octave as a foreign black box
using pipes for communication. This approach is bound to fail with each new
version. Any fix made to make them work with a new Octave versions would only
be temporary. This included QtOctave (now abandoned and incompatible with
newer versions of Octave), Xoctave (which is proprietary and commercial), and
GUI Octave (which was proprietary and no longer available).
The previously existing GUIs were not part of Octave itself. The integration within Octave was rather bad, as all of them treated Octave as a foreign black box and used pipes for communication. This approach is bound to fail with each new version of Octave, as any fix would only be temporary. For historical reasons and to honor the approaches, a short list of previous GUIs for Octave: * '''QtOctave''' was a great, beautiful, and very useful tool which is now abandoned and incompatible with newer versions of Octave. We are thankful to its developers to make it free software so we could reuse large chunks of it for what is now the Octave GUI. * '''Quint ''' was a project for an Octave GUI that actually tried to do it right. Eventually [https://lists.gnu.org/archive/html/octave-maintainers/2011-07/msg00096.html it was merged into the Octave repository ] and is no longer aseparate project. Also, many bits from QtOctave were reused in the GUI.
QtOctave was a great and very useful tool* '''[http://www. It looked beautiful and we arethankful to its developers for working on such a nice toolxoctave. However, itwould have 'com/ Xoctave]'never'' been stable as it was. But most of all, the developersmade it free software so we could reuse large chunks of it which wereincorporated in what is now the Octave GUIproprietary and commercial.
* '''GUI Octave''', which was proprietary and is no longer available.
=Graphics: backends and toolkits=
==What are the supported graphics backends?==
The * [https://www.opengl.org/ OpenGL] via the graphics toolkits '''[https://www.qt.io/ qt]''' (current default is OpenGL, through ) and '''[http://www.fltk.org/ fltk]'''* [http://www.gnuplot.info/ gnuplot] via the "qt" '''gnuplot''' graphics toolkit. The "ftlk"  ==How do I change my graphics toolkit also relies on OpenGL.?== There are three commands to deal with graphics toolkits:
Alternatively, Gnuplot can be {| class="wikitable"| <code>available_graphics_toolkits</code>| lists all available graphics toolkits|-| <code>graphics_toolkit</code>| displays the currently used as a graphics backend by selecting the toolkit|-| <code>graphics_toolkit ("qt/fltk/gnuplot" )</code>| sets the graphics toolkitto either of [https://www.qt.io/ qt], [http://www.fltk.org/ fltk], or [http://www.gnuplot.info/ gnuplot], if available|}
==Why did you replace Gnuplot gnuplot with an OpenGL backend?==
The development of Octave is committed to being both compatible with Matlab and adding additional features. Toward those ends, the development community has chosen developers decided to introduce a native OpenGL backend that supports Matlab handle graphics and its uicontrols. Starting with the 3.8 release, Octave uses OpenGL graphics by default (with [http://www.fltk.org/ FLTK widgets ] in Octave 3.8 and [https://www.qt.io/ Qt widgets ] in Octave 4.0 and later).
==Are there any plans to remove the gnuplot backend?==
'''No.''' There are no plans to remove the gnuplot backend. Even though the default graphics toolkit is now "qt", which uses OpenGL graphics with Qt widgets, the gnuplot backend It will still be available as long as our users find it useful.
==How can I implement a new graphics backend/toolkit?==