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This is a list of frequently asked questions (FAQ) for GNU Octave users.
This is a list of frequently asked questions (FAQ) for Octave users.


We are always looking for new questions (with answers), better answers, or both. Feel free to edit this page with your changes.
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.


=Where do I get additional help?=
This FAQ is intended to supplement, not replace, the Octave manual. Before posting a question to the help@octave.org mailing list, you should first check to see if the topic is covered in the manual.


If you can't find an answer to your question in this FAQ, wiki, or in the [http://www.octave.org/doc/interpreter manual] ([http://www.octave.org/octave.pdf PDF]) you can:
=General=
 
==What is Octave?==
 
Octave is a high-level interactive language, primarily intended for numerical computations that is mostly compatible with Matlab.
 
Octave can do arithmetic for real, complex or integer-valued scalars and matrices, solve sets of nonlinear algebraic equations, integrate functions over finite and infinite intervals, and integrate systems of ordinary differential and differential-algebraic equations.
 
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.
 
The Octave distribution includes a 650+ page Texinfo manual. Access to the complete text of the manual is available via the doc command at the Octave prompt.
 
==What is Octave Forge?==
[http://octave.sourceforge.net/ 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 refered to Octave core (or just ''core''). It also serves as a testbed for code that may eventually end up in Octave, and distributes binaries for systems with a lack of developers tools (mainly windows).


* Search for an answer in our [https://lists.gnu.org/archive/html/help-octave/ mailing list archives]
==Who uses Octave?==
* Contact our user community using our [https://octave.discourse.group Octave Discourse].
* Contact our user community using our [https://webchat.freenode.net/?channels=octave IRC chat room <code>#octave</code> in Freenode]


<div class="tocinline">__TOC__</div>
Lots of people. It seems that universities use it for research and teaching, companies of all sizes, for development, individuals. This question comes often on Octave mailing lists, see [[Who Uses Octave?]] for a few answers


=== Support expectations ===
==Who develops Octave?==
See [https://octave.org/support-expectations.html Support Expectations]


Also this [https://www.commitstrip.com/en/2014/05/07/the-truth-behind-open-source-apps/ CommitStrip]
Discussions about writing the software that would eventually become Octave started in about 1988 with James B. Rawlings and John W. Eaton at the University of Texas. John W. Eaton was the original author of Octave, starting full-time development in February 1992. He is still the primary maintainer. The community of users/developers has in addition contributed some code and fuels the discussion on the mailing lists help@octave.org (user forum), maintainers@octave.org (development issues).


=General=
==Why "Octave"?==
 
Octave's name has nothing to do with music. It's 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 that Mr Levenspiel could do so.
 
==Why <em>GNU</em> Octave?==


==What is Octave?==
The GNU Project was launched in 1984 to develop a complete Unix-like operating system which is free software: the GNU system.


[https://www.gnu.org/software/octave/ GNU Octave] is a high-level interpreted language, primarily intended for numerical computations.  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.
GNU is a recursive acronym for “GNU's Not Unix”; it is pronounced guh-noo, approximately like canoe.
The GNU Octave language is quite similar to Matlab so that most programs are easily portable.


The GNU Octave distribution includes a [http://www.octave.org/octave.pdf 1000+ page Texinfo manual].  Access to the complete text of the manual is available via the <code>doc</code> command at the GNU Octave prompt.
The Free Software Foundation (FSF) is the principal organizational sponsor of the GNU Project.


==What is Octave Forge?==
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.


[https://octave.sourceforge.io/ 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").  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).
For more information about the GNU project, see http://www.gnu.org.


==Who uses Octave?==
==What version should I use?==


A huge number of people ranging from students to researchers involved in various fields such as statistics, Machine Learning, data analytics, etc. Universities use it for research and teaching, companies of all sizes for development and individuals for certain private purposes. See [[Who Uses Octave?]] for more clarity.
In general, you will find the latest version on http://www.octave.org/download.html. It 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.


==Who develops Octave?==
A list of user-visible changes since the last release is available in the file NEWS. The file ChangeLog in the source distribution contains a more detailed record of changes made since the last release.


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 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). Since 2011, GNU Octave regularly  participates in [[Summer of Code]] events as a mentor organisation. As part of those events, several students contributed to Octave by helping in removal of bugs and development of new features.
==On what platforms does Octave run?==


==Why "Octave"?==
Octave runs on various Unices—at least Linux and Solaris, Mac OS X, Windows and anything you can compile it on. 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 7.


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 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.
Two and three dimensional plotting is fully supported using gnuplot and an experimental OpenGL backend.


==Why "GNU" Octave?==
The underlying numerical solvers are currently standard Fortran ones like LAPACK, LINPACK, ODEPACK, the BLAS, etc., packaged in a library of C++ classes. If possible, the Fortran subroutines are compiled with the system's Fortran compiler, and called directly from the C++ functions. If that's not possible, you can still compile Octave if you have the free Fortran to C translator f2c.


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].
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.


The [https://www.fsf.org/ Free Software Foundation (FSF)] is the principal organization that has sponsored the GNU Project.
==Why are the developers planning to replace Gnuplot with an OpenGL backend?==


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 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 fundHowever, Octave is not and has never been developed by the FSF.
The development of Octave is committed to being both compatible with Matlab and adding additional features. Toward those ends, the development community has chosen to introduce a native OpenGL backend that supports Matlab handle graphics and its uicontrols. The introduction of the experimental fltk graphics toolkit is the first product of this effort. As of the 3.6.N series, the fltk toolkit is approximately as advanced as is the Gnuplot toolkitIt is not yet decided if the fltk toolkit is to become the default backend, or if another OpenGL implementation will replace Gnuplot as the default backend (An QtOpenGL toolkit is also under development).


==How can I cite Octave?==
==How can I cite Octave?==


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 Octave, and we would appreciate if you would cite if you usedTo cite GNU Octave in publications use:
Pointing to http://www.octave.org is good, because that gives people a direct way to find out more. If citation of a URL is allowed by the publisher you can use this entry:
 
    <nowiki>@MISC{octave:2012,
    author = {{Octave community}},
    keywords = {Octave,Software},
    title = {{GNU/Octave}},
    url = {www.gnu.org/software/octave/},
    year = {2012}
    }</nowiki>
 
if you also want to point to a traditional reference, then you can cite the Octave manual:
 
    @BOOK{eaton:2008,
      author =    "John W. Eaton, David Bateman, and Søren Hauberg",
      title =      "GNU Octave Manual Version 3",
      publisher = "Network Theory Limited",
      year =      "2008",
      isbn =      "0-9546120-6-X"
    }
 
 
If you want to acknowledge Octave instead of citing it, you can use text such as this:
 
<blockquote>
The data has been numerically analyzed with the free software package GNU Octave.
</blockquote>
 
or


  John W. Eaton, David Bateman, Søren Hauberg, Rik Wehbring ({{Release Year}}).
<blockquote>
  GNU Octave version {{Release}} manual: a high-level interactive language for numerical computations.
This work made use of the free software package GNU Octave, and the authors are grateful for the support of the Octave development community.
  URL https://octave.org/doc/v{{Release}}/
</blockquote>


A [https://en.wikipedia.org/wiki/BibTeX BibTeX] entry for [https://en.wikipedia.org/wiki/LaTeX LaTeX] users is:
==How can I get involved in Octave development?==


  @manual{,
Be around. Be social. Participate in the help and maintainers' mailing lists. 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 whole, but it also prepares you to be a better Octave contributor.
    title    = {{GNU Octave} version {{Release}} manual: a high-level interactive language for numerical computations},
 
    author    = {John W. Eaton and David Bateman and S{\o}ren Hauberg and Rik Wehbring},
If you feel ready to dive right into the code, [http://www.gnu.org/software/octave/get-involved.html here are some instructions on how to do so]. Make sure you read {{Path|etc/HACKING}} for guidance.
    year      = <span>{</span>{{Release Year}}},
 
    url      = {[https://octave.org/doc/v{{Release}}/ https://octave.org/doc/v{{Release}}/]},
We also need help with this wiki and the manual. These are also important tasks. The documentation is easier to patch, so you can discuss improvements to it and submit patches. Or just edit this wiki! Accurate bug reporting is also very useful. Find and report bugs, making an attempt to diagnose them. Eventually, you will also know how to fix them.
  }


Run {{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>.
If you want to help with bug reports or patches, subscribe to [https://savannah.gnu.org/mail/?group=octave the bug tracker mailing list]. You'll get updates on all bug activity, and you can jump in when you see something you can help with.


Note that there are two reasons for citing the software used.  One is giving recognition to the work done by others which we have already addressed to. The other is giving details on the system used so that experiments can be replicated.  For this, you should cite the version of Octave and all packages used (you can get this information using the <code>ver</code> command), as well as any details of your setup as part of your Methods.  In addition, you should make your source available as well. See [http://software.ac.uk/so-exactly-what-software-did-you-use How to cite and describe software] for more details and an in depth discussion for the same.
Also look at our [[Projects]], the [[ESA Summer of Code in Space]], and [[GSoC Project Ideas|GSoC Project]] ideas if you need specific inspiration for coding tasks that we would like to get done.


==What documentation exists for Octave?==
=Licensing issues=


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.
==If I write code using Octave do I have to release it under the GPL?==


==How can I report a bug in Octave?==
The answer depends on precisely how the code is written and how it works.


Please read our website http://www.octave.org/bugs.html.
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 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.


= Common problems =
Code written using 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:


== Octave does not start ==
# The plugin should not use any bindings that are specific to 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.


The following steps have been the solution to several bug reports and help requests. Please try them before asking for further support. If nothing below helps, please give us the following information:
A program that embeds the Octave interpreter (e.g., by calling the "octave_main" 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.


* Operating system: e.g. [https://support.microsoft.com/en-us/help/13443/windows-which-version-am-i-running '''MS Windows 10 (version 2004)'''] or '''Ubuntu 20.04'''
==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?==
* GNU Octave version: e.g. '''Version {{Release}}'''
* Installation method: e.g. '''Downloaded and installed "octave-{{Release}}-w64-installer.exe" from https://www.octave.org/download.html'''


=== MS Windows ===
No. The original reason for implementing the MEX interface for Octave was to allow Octave to run free software that uses MEX files (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 for Octave. For the good of the community, we strongly encourage users of Octave to release the code they write for Octave under terms that are compatible with the GPL.


* After Octave upgrade the GUI does not open / shuts down immediately.
==I wrote a program that links with Octave libraries and I don't want to release it under the terms of the GPL. Will you change the license of the Octave libraries for me?==
** '''Solution:'''
*** Version 5.2.0 and older: Delete the folder {{path|C:\Users\YOUR_USER_NAME\.config\octave}}
*** Version 6.1.0 and newer: Delete the folder {{path|%APPDATA%\octave}}, which generally is located at {{path|C:\Users\YOUR_USER_NAME\AppData\Roaming\octave}}
* Missing/conflicting files.
** '''Solution:''' Remove/Uninstall all existing Octave versions.  Restart the system.  Install GNU Octave again.


* Permission errors
No. Instead of asking us to change the licensing terms for Octave, 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 Octave.
** '''Solution 1:''' Octave versions prior to version 7.1.0 on MS Windows used VBS scripts to start the program.  You can test whether your system is blocking VBS scripts by doing the following:
**# Using Notepad or another text editor, create a text file containing only the text: <pre>msgbox("This is a test script, Click OK to close")</pre>
**# Save the file on your Desktop with the name {{Path|testscript.vbs}} (be sure that the editor didn't end it in .txt or .vbs.txt).
**# Double click the file.  If scripts can run, a popup window will appear with that message.
**#* If the file opens in notepad or an editor, it means it still ended in .txt.  MS Windows insecurely hides file extensions by default.  To show file extensions follow [https://answers.microsoft.com/en-us/windows/forum/all/in-win10-how-to-show-the-file-extension-for/ed21ff20-cdb3-4263-9c7d-fc6ed125fc82 these instructions at Microsoft.com].
**#* If both {{Path|testscript.vbs}} and {{Path|octave.vbs}} open a text- or other editor, it means your MS Windows file associations have .vbs files associated with another program.  To fix this, right click the .vbs file, select "Open With", select "Choose Another App", check the box that says "Always use this app to open .vbs files".  Finally, select "Microsoft Windows Based Script Host" from the list.  If it is not in the list, select "More apps".  If still not there, select "Look for Another App on this PC" and navigate to {{Path|C:\Windows\System32\wscript.exe}}, select it, and select "Open".  If {{Path|wscript}} is still not present you will need to seek assistance installing missing MS Windows components.
**# Try moving {{Path|testscript.vbs}} to another location, such as a {{Path|C:\temp folder}}.  Additionally try to move {{Path|testscript.vbs}} in the Octave installation folder containing {{Path|octave.vbs}} and see if VBS scripts can be run there.
**# If {{Path|testscript.vbs}} doesn't run in any of those locations, then scripting appears to be disabled or blocked on your system.  If {{Path|testscript.vbs}} runs in some locations but not others, there there may be other security permissions errors to be solved.  If {{Path|testscript.vbs}} runs in the same folder as {{Path|octave.vbs}}, but directly double-clicking on {{Path|octave.vbs}} does not start Octave, then there appears to be some problem other than script permissions.
** '''Solution 2:''' Consult your malware detection (a.k.a. AntiVirus) software, if files are blocked.
** '''Solution 3:''' Did you install Octave on a network-drive?  Do you have the execution permissions?
** '''Solution 4:''' Is your computer managed by your company?  Does your administrator prohibit script execution?
===Collecting gdb backtrace information===
The following instructions can help you gather troubleshooting information that may help developers identify the problem if the above steps are ineffective:
* if Octave is 'hanging' (the process is remaining open):
*# attempt to start the Octave GUI
*# with the program stalled (either at the GUI, or with the black terminal window), open the Task Manager (right click on taskbar, select Task manager), switch to the "Details" tab, find `octave-gui.exe` on that list, ad take note of the corresponding PID (process ID)
*# Open the folder where Octave is installed. You should find a file called `cmdshell.bat` in the main folder. Run that file, which should open a MSYS2 bash (command line) window.
*# At that prompt, run `gdb -p <em>PID</em>` where <em>PID</em> is the process ID noted previously.
*# at the gdb prompt, execute `set logging on` to save all output to a text file (default will be `gdb.txt`. If you want a different location or filename you can execute `set logging file C:\path\to\file.txt` first).
*# execute `thread apply all bt`.  (If this returns a list longer than one page you may need to 'continue' by typing `c`.)
*# execute `quit` to leave gdb.
*# append that text file to your trouble report at octave.discourse.group or bug report at bugs.octave.org.


* if Octave is immediately crashing and closing:
==Why can't I use code from File Exchange in Octave? It's released under a BSD license!==
*# Open the folder where Octave is installed. You should find a file called `cmdshell.bat` in the main folder. Run that file, which should open a MSYS2 bash (command line) window.
*# At that prompt, run `gdb octave`. (that will start gdb attached to the octave executable.)
*# at the gdb prompt, execute `set logging on` to save all output to a text file (default will be `gdb.txt`. If you want a different location or filename you can execute `set logging file C:\path\to\file.txt` first).
*# At the gdb prompt, execute `r --gui`.  That should attempt to start the Octave in GUI mode.  The gdb prompt should stay unresponsive as long as octave is running.
*# If octave crashes, the gdb prompt should become responsive again. execute `thread apply all bt`.  (If this returns a list longer than one page you may need to 'continue' by typing `c`.)
*# append the text file to your trouble report at octave.discourse.group or bug report at bugs.octave.org.


==I do not see any output of my script until it has finished?==
When one downloads code 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 code in Octave, it also allows others to further impose restrictions which Mathworks does through the terms of Use of their site.:


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 [https://www.octave.org/doc/interpreter/Paging-Screen-Output.html in the manual].
{{quote|text=Content submitted to File Exchange may only be used with MathWorks products.|sign=Matlab central|source=[http://www.mathworks.co.uk/matlabcentral/termsofuse.html#content Terms of Use 2iii]}}


==When I try plotting from a script, why am I not seeing anything?==
While interpretations of this vary, it should be safe to use the code if you contact the author directly and have them send you the code personally.


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).
=What's new in Octave=
==What's new in version series 3.6.N and 3.7.N of Octave==


A common solution is to put a {{manual|pause}} command at the end of your script.
Several new features have been added to the 3.6.N series. The full details are in the NEWS file, but in brief 3.6.N series brings:


==How do I get sound input or output in MS Windows?==
* Perl compatible regular expressions
* A profiler has been added.
* Broadcasting enabled for all built-in binary element-wise operators.
* The statistical distribution functions have been overhauled.
* The functions strread(), textscan(), and textread() have been rewritten.
* Performance of all m-file string functions has been improved.
* The qhull geometry functions have been revamped.
* Date/time functions have been updated.
* Matlab compatible preference functions have been added.
* Various handle graphics functions have be introduced.
* The parfor keyword is now recognized.


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 have problems with the [https://www.octave.org/doc/interpreter/Audio-Processing.html audio I/O functions] using Octave 4.0.0 or a newer version, please report them on the [http://bugs.octave.org bug tracker].
==Features added in version series 3.4.N and 3.5.N of Octave==
Here are some features that have been around since 3.4.N


==I have problem X using the latest Octave version==
* Many improvements to native OpenGL plotting
* ARPACK now distributed 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 a single LAPACK call
* Other optimisations in matrix operations
* bsxfun optimised for basic arithmetic functions
* Matlab-style ignoring of output arguments using {{Codeline|~}}
* Many optimisations 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 compatibility


Please be more specific about what you mean by "latest version"?
==Features added in version series 3.2.N and 3.3.N of Octave==
Here are some features that have been around since 3.2.N


* The latest stable version is {{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 the following as in accordance to your Operating system: [[Octave for GNU/Linux|GNU/Linux]], [[Octave for macOS|macOS]], or [[Octave for Microsoft Windows|Windows]].
* 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.


* If you refer to the latest Mercurial revision, please specify the [https://www.mercurial-scm.org/wiki/ChangeSetID changeset ID] not the revision number, e.g. the output of <code>hg summary</code> or <code>hg id</code>.  Changeset IDs are globally unique across all repos.
==Features available since 2.1.N==
Here are some older features that have been around since 2.1.N:


If your problem still persists with the "latest version", then please [http://bugs.octave.org/ report a bug] or ask for help at [https://lists.gnu.org/mailman/listinfo/help-octave help@octave.org].  Otherwise, don't be surprised if volunteers are less inclined to help you with a problem that only exists in an older version of Octave and is already fixed in a newer version.
* NDArrays
* cells


==Why is Octave's floating-point computation wrong?==
==Coming in a future release==
The 3.7.N series is the current development release and will become a 3.8.N release in the future. This series brings the following new features:


Floating-point arithmetic is an approximation '''in binary''' to arithmetic on real or complex numbers.  Just like you cannot represent 1/3 exactly in decimal arithmetic (0.333333... is only a rough approximation to 1/3 for any finite number of 3s), you cannot represent some fractions like <math>1/10</math> exactly in base 2. In binary, the representation to one tenth is <math>0.0\overline{0011}_b</math> where the bar indicates that it repeats infinitely (like how <math>1/6 = 0.1\overline{6}_d</math> 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 - 0.2 - 0.1 is not equal to zero.
* JIT compiling in the interpreter (speeds up loops)
* A GUI for Octave (based on Qt4)
* The default graphics toolkit it planned to be changed from Gnuplot to an OpenGL fltk toolkit.


In addition, some advanced operations are computed by approximation and there is no guarantee for them to be accurate, see [https://en.wikipedia.org/wiki/Rounding#Table-maker.27s_dilemma Table-maker's dilemma] for further references. Their results are system-dependent.
=What documentation exists for Octave?=


This isn't a bug that is limited to GNU-Octave & 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 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.
Besides the current wiki, there are other important sources of documentation and help for Octave.


Another approach to deal with rounding errors is interval arithmetic with the [[Interval package]] or symbolic computations with the [[Symbolic package]].  These approaches are likely to be slower, since not all operations can be performed on Hardware like pure floating-point arithmetic.
==What documentation exists for Octave?==


To learn more about floating-point arithmetic, consult this [https://en.wikipedia.org/wiki/Floating-point_arithmetic Wikipedia article] or the classical reference by David Goldberg [http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html What Every Computer Scientist Should Know About Floating-Point Arithmetic].
The Octave distribution includes a 650+ page manual that is also distributed under the terms of the GNU GPL. It is available on the web at http://www.gnu.org/software/octave/doc/interpreter/ and you will also find there instructions on how to order a paper version.


==Missing lines when printing under Windows with OpenGL toolkit and Intel integrated GPU==
The complete text of the Octave manual is also available using the GNU Info system via the GNU Emacs, info, or xinfo programs, or by using the {{Codeline|doc}} command to start the GNU info browser directly from the Octave prompt.


Some windows users with integrated Intel GPUs have reported missing lines when printing with an OpenGL toolkit like FLTK or Qt. {{bug|42534}}
If you have problems using this documentation, or find that some topic is not adequately explained, indexed, or cross-referenced, please report it on http://bugs.octave.org.


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.
==Getting additional help==


See also https://www.opengl.org/wiki/FAQ#Why_is_my_GL_version_only_1.4_or_lower.3F .
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 Octave that are not adequately answered by the Octave manual or by this document.


==Plot hangs and makes the GUI unresponsive==
==User community==


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}}
To subscribe to the list, go to http://www.octave.org/archive.html and follow the link to the subscription page for the list.


==Error message about invalid call to script or invalid use of script in index expression==
Please do not send requests to be added or removed from the mailing list, or other administrative trivia to the list itself.


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 same global namespace. It is best to avoid creating your own scripts or functions that have the same name as an Octave function as to avoid this error regarding the invalid call to script or invalid use of script in index expression.
An archive of old postings to the help-octave mailing list is maintained on http://www.octave.org/archive.html.


=Licensing issues=
You will also find some user advice and code spread over the web. Good starting points are the Octave Wiki http://wiki.octave.org and Octave-Forge http://octave.sourceforge.net


==If I write code using Octave do I have to release it under the GPL?==
We also have [http://www.octave.org/chat.html an IRC chat room].


The answer depends on precisely how the code is written and how it works:
==I think I have found a bug in Octave.==


* 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.
“I think I have found a bug in Octave, but I'm not sure. How do I know, and who should I tell?”


* 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 internals and is considered a derivative work of Octave. Therefore it must be released under terms that are compatible with the [https://www.gnu.org/licenses/gpl.html GPL].
First, see the section [http://www.octave.org/bugs.html on bugs and bug reports in the 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 the version of Octave that you are using. Also provide enough code and configuration details of your operating system so that the Octave maintainers can duplicate your bug.


* 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:
=How can I obtain Octave?=


:# The MEX file may not use any bindings that are specific to Octave, '''it has to use the MEX interface only'''.  In other words, 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].
==Source code==
:# The MEX file 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 to effectively create a single work.


* 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.
Source code is available on the Octave development site, where you are sure to get the latest version.


==Will you change the license of the Octave libraries for me?==
* http://www.octave.org/download.html
* ftp://ftp.octave.org/pub/octave/


'''No.''' Instead of asking us to change the licensing terms for Octave, we recommend that you release your program under terms that are compatible with the GPL, this way the free software community can be benefited from your work the same as you were/have benefited from the work of all the people who have contributed to Octave.
Since Octave is distributed under the terms of the GPL, you can get Octave from a friend who has a copy, or from the Octave website.


==Should I favor the MEX interface to avoid the GPL?==
==Pre-compiled binary packages==


'''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 softwares available to Octave users & not to enable people to write proprietary code for Octave. For the good of the community, we 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].
The Octave project does not distribute binary packages, but other projects do. For an up-to-date listing of packagers, see:


==Why can't I use code from File Exchange in Octave?==
* http://www.octave.org/download.html
* [[Build From Source]]


According to the Matlab Central [https://www.mathworks.com/matlabcentral/termsofuse.html Terms of Use] (Last updated: 10-Aug-2016), all submitted code is licensed under the [https://en.wikipedia.org/wiki/BSD_licenses BSD license] by default (cf. § 5 [https://www.mathworks.com/matlabcentral/termsofuse.html Terms of Use]), but it is clearly stated that:
As 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.


{{Quote|text=Content submitted to File Exchange may only be used with MathWorks products. | |§ 2(a)(iii) [https://www.mathworks.com/matlabcentral/termsofuse.html Terms of Use]}}
==How do I get a copy of Octave for (some other platform)?==


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 purpose]].
Octave currently runs on Unix-like systems, Mac OS X, and 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 [mailto:maintainers@octave.org the maintainers' mailing list].


=Installation=
=Installation issues and problems=  


==How can I install Octave on Windows?==
Octave 3.4 requires approximately 1.3 GB of disk storage to unpack and compile from source (considerably less if you don't compile with debugging symbols). Once installed, Octave requires approximately 355 MB of disk space (again, considerably less if you don't compile with debugging symbols, approximately 50 MB).


:'' So as to install GNU-Octave for Windows O.S, refer to : [[Octave for Microsoft Windows]]''
Check out the page [[Installation]] for more detailed information about installing Octave.


==How can I install Octave on MacOS?==
==What else do I need?==


:''So as to install GNU-Octave for MacOS, refer to : [[Octave for macOS]]''
To compile Octave, you will need a recent version of GNU Make. You will also need GCC 4.3 or later, although GCC 4.4 or later is recommended.


==How can I install Octave on GNU/Linux?==
'''You must have GNU Make to compile octave'''. Octave's Makefiles use features of GNU Make that are not present in other versions of make. GNU Make is very portable and easy to install.


:'' So as to install GNU-Octave on GNU/Linux, refer to: [[Octave for GNU/Linux]]''
==Can I compile Octave with another C++ compiler?==


==How to install Octave on Android OR What is the Octave app available in the Google Play store?==
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 the http://bugs.octave.org bug tracker, or ask for help on the [mailto:help@octave.org mailing list].


There is an '''unofficial''' Octave app available for Android in the Google Play store. Please see [[Octave for Android]] for further  information.
== How do I install ''all'' Octave packages? ==
Do not do it! Really, there is no reason to do this. Octave Forge has many packages for different needs but it's unlikely that you need all of them. The common misconception is that the more packages one installs, the more complete and powerful its octave installation will be be. However, in the same way one would ''never'' install all perl modules, ruby gems or python packages (because it simply makes no sense), one should not install all octave packages. This isn't desirable and it's not even possible.


==How can I install Octave on platform X?==
Packages should be installed and loaded selectively. Note that some packages are meant to shadow core functions changing the way Octave works, and different packages can have different implementations of a function with the same name, leading to unpredictable results. Others are just broken or crappy and will break your system. What's worse, some of them packages are even loaded automatically at startup so you may be screwing your octave installation without even realizing it.


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].
=Coding=


==What Octave version should I use?==
==What features are unique to Octave?==


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/.
Although most of the Octave language will be familiar to Matlab users, it has some unique features of its own.


The used version of Octave is available via the {{manual|ver}} command and a list of user-visible changes since the last release is available via the {{manual|news}} command at the GNU Octave prompt.
=== 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:


==On what platforms does Octave run?==
    octave:1> function s = hello_string (to_who)
    > ## Say hello
    > if nargin<1, to_who = "World"; end
    > s = ["Hello ",\
    >      to_who];
    > endfunction
    octave:2> hello_string ("Moon")
    ans = Hello Moon


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 underlying 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., and for plotting [https://www.opengl.org/ OpenGL] or [http://www.gnuplot.info/ gnuplot].
As a natural extension of this, functions can also be defined in script files (m-files whose first non-comment line isn't {{Codeline|function out &#61; foo (...)}})


==How can I obtain Octave's source code?==
===Comments with #===


The latest version of the Octave source code (and older versions) is available from:
The pound character, {{Codeline|#}}, may be used to start comments, in addition to {{Codeline|%}}. See the previous example. The major advantage of this is that as {{Codeline|#}} is also a comment character for unix script files, any file that starts with a string like {{Codeline|#! /usr/bin/octave -q}} will be treated as an octave script and be executed by octave.


* https://www.octave.org/download.html
===Strings delimited by double quotes "===
* https://ftp.gnu.org/gnu/octave/


Since Octave is distributed under the terms of the GPL, you can get Octave from a friend who has a copy.
The double quote, {{Codeline|"}}, may be used to delimit strings, in addition to the single quote {{Codeline|'}}. 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).


==How can I build Octave from the source code?==
===Line continuation by backslash===


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]].
Lines can be continued with a backslash, {{Codeline|\}}, in addition to three points {{Codeline|...}}. See the previous example.


If you have reasons to build Octave from the source code, see [[Building]] for more information.
===Informative block closing===


==What do I need to build Octave from the source code?==
You may close function, 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.


For a list of build dependencies, refer to  [[Building]].
===Coherent syntax===


==Do I need GCC to build Octave from the source code?==
Indexing other things than variables is possible, as in:


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 known to work as well).  If you face any 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-octave help@octave.org mailing list].
    octave:1> [3 1 4 1 5 9](3)
    ans = 4
    octave:2> cos([0 pi pi/4 7])(3)
    ans = 0.70711


=What's new in Octave?=
In Matlab, it is for example necessary to assign the intermediate result {{Codeline|cos([0 pi pi/4 7])}} to a variable before it can be indexed again.


Each new 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.
===Exclamation mark as not operator===


* '''What's new in the next version of Octave?'''
The exclamation mark {{Codeline|!}} (aka “Bang!”) is a negation operator, just like the tilde {{Codeline|~}}:
** See the [https://hg.savannah.gnu.org/hgweb/octave/file/tip/NEWS NEWS file] on the development branch.
* '''What was new in Octave Version X.Y.Z?'''
** See [[Release History]].


=Packages and Octave Forge=
    octave:1> if ! strcmp (program_name, "octave"),
    >  "It's an error"
    > else
    >  "It works!"
    > end
    ans = It works!
Note however that Matlab uses the {{Codeline|!}} operator for shell escapes, for which Octave requires using the system command.


==How do I install or load all Octave Forge packages?==
===Increment and decrement operators===


Do not do it! Really, there is no reason to do this. Octave has many packages for different needs and is unlikely that you need all of them. You either have a small set of required packages, in which case
If you like the {{Codeline|++}}, {{Codeline|+&#61;}} etc operators, rejoice! Octave includes the C-like increment and decrement operators {{Codeline|++}} and {{Codeline|--}} in both their prefix and postfix forms, in addition to {{Codeline|+-}}, {{Codeline|-&#61;}}, {{Codeline|*&#61;}}, {{Codeline|/&#61;}}, {{Codeline|^&#61;}}, {{Codeline|.*&#61;}}, {{Codeline|./&#61;}}, and {{Codeline|.^&#61;}}.
you know them by name; or you want them all "just because", in which case you don't really need them.


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 install all Octave packages.
For example, to pre-increment the variable x, you would write {{Codeline|++x}}. This would add one to x and then return the new value of x as the result of the expression. It is exactly the same as the expression {{Codeline|x &#61; x + 1}}.


Packages should be installed and loaded selectively. Note that some packages are meant to shadow core functions changing the way Octave works, and that different packages can have different functions with the same name leading to unpredictable results.
To post-increment a variable x, you would write {{Codeline|x++}}. This adds one to the variable x, but returns the value that x had prior to incrementing it. For example, if x is equal to 2, the result of the expression x++ is 2, and the new value of x is 3.


If you really really really want to do load all packages, you can with the following:
For matrix and vector arguments, the increment and decrement operators work on each element of the operand.
<syntaxhighlight lang="octave">
## WARNING: loading all packages is probably not the solution you are looking for.
cellfun (@(x) pkg ("load", x.name), pkg ("list"));
</syntaxhighlight>


==I have installed a package but still get a "foo undefined" error?==
===Unwind-protect===


You have probably forgotten to load the package.  Use {{Codeline|pkg load package-name}} to load it.  Most packages are no longer loaded automatically to avoid surprises.  See reasoning on related FAQ [[FAQ#How_do_I_install_all_Octave_packages.3F|how do I install all Octave packages]].  If you want a specific package to be loaded by default at startup, consider adding the {{Codeline|pkg load}} command on your {{path|[[.octaverc]]}} file.
In addition to try-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:


==I cannot install a package. Octave complains about a missing mkoctfile.==
    unwind_protect
      body
    unwind_protect_cleanup
      cleanup
    end_unwind_protect


You should normally use your distribution's packages.  For Debian and Fedora, Octave package <code>foo</code> will be a deb or rpm called <code>octave-foo</code>, and you should install that instead using <code>apt</code> or <code>yum</code>.
Where body and cleanup are both optional and may contain any Octave expressions or commands. The statements in cleanup are guaranteed to be executed regardless of how control exits body.


If you really need to build Octave packages from source to install them, you'll need {{manual|mkoctfile}}. Most distributions split Octave into several packages.  The script {{manual|mkoctfile}} is then part of a separate package:
The unwind_protect statement is often used to reliably restore the values of global variables that need to be temporarily changed.


* Debian/Ubuntu: [https://packages.debian.org/stretch/liboctave-dev liboctave-dev]
Matlab can be made to do something similar with their {{Codeline|OnCleanUp}} function that was introduced in 2008a. Octave also has {{Codeline|onCleanup}} since version 3.4.0.


* Fedora: {{Codeline|octave-devel}}
===Built-in ODE and DAE solvers===


==How do I automatically load a package at Octave startup?==
Octave includes LSODE, DASSL and DASPK for solving systems of stiff ordinary differential and differential-algebraic equations. These functions are built in to the interpreter.


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 it.  If the files does not exist, create it.
==How does Octave solve linear systems?==


If you do this, remember that other people may not have Octave configured to load packages at startup. Therefore, if you write code for others, remember that your programs still need to load the packages they require.
In addition to consulting Octave's source for the precise details, you can read 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 {{Codeline|A\x}} will be interpreted. Sections [http://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.


=Octave usage=
=How do I...?=


==How do I execute an Octave script?==
==How do I execute an Octave script?==


First of all, make sure you understand [http://www.octave.org/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>
First of all, make sure you understand [http://www.gnu.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 {{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}}.
To execute a script from within Octave, just type its name without the .m extension. Thus, if you have a script called <code>foo.m</code>, just type <code>foo</code> from within Octave to execute it. You have to make sure that the script is in your current path. Type <code>path</code> in Octave to see what this path is.


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 {{manual|run}} function instead:
If the script name has characters that are not valid for an Octave identifier, or if you do not want to use addpath to add the script's location to the current path, you can use the <code>run</code> function instead:


<syntaxhighlight lang="octave">
  octave> run("Script Name With Spaces.m")
run ("Script Name With Spaces.m")
  octave> run("/opt/local/foo.m")
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 {{manual|argv}} command:
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>argv</code> command:


   $ octave the-script.m arg1 arg2
   $ octave the-script.m arg1 arg2
Line 343: Line 409:
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]].
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 I close a figure?==  
==do xxxx?==
 
You are probably looking for 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 the octave prompt for more). The following example helps to find the function to calculate correlation coefficient in a matrix:
 
  octave:1> lookfor ("correlation")
  corr2              Returns the correlation coefficient between 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 the autocorrelations from lag 0 to H 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:
 
  octave:2> corr
  corr2    corrcoef


To close the current figure type {{manual|close}} in the Octave command prompt.
==How do I erase a figure?==
 
closeplot();
closefig(number)


==How do I set the number of displayed decimals?==
==How do I set the number of displayed decimals?==


You can control the number of displayed decimals using the {{manual|format}} command:
    octave:1> format long
    octave:2> pi
    pi = 3.14159265358979
    octave:3> format short
    octave:4> pi
    pi = 3.1416


<syntaxhighlight lang="octave">
==How do I call an octave function from C++?==
>> format long
>> pi
pi = 3.14159265358979
>> format short
>> pi
pi = 3.1416
</syntaxhighlight>


==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:


Please read the manual https://www.gnu.org/software/octave/doc/interpreter/Calling-Octave-Functions-from-Oct_002dFiles.html.
#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 color/line definition in gnuplot postscript?==
==How do I change colour/line definition in gnuplot postscript?==
 
Here is a awk script to get a rainbow colour map
Here is a awk script to get a rainbow color map


  #!/bin/awk -f
  #!/bin/awk -f
Line 404: Line 492:
==How do I tell if a file exists?==
==How do I tell if a file exists?==


One can use the function {{manual|exist}} to tell if a regular file, say <code>foo.txt</code> exist in Octave's load path, or the current directory:
Look at functions like exist, file_in_path.. and 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)?==
 
  figure(1, "visible", "off");
  plot(sin(1:100));
  print -deps "/tmp/sin.eps"
 
One can set that behaviour as default:
 
  set(0, 'defaultfigurevisible', 'off');
 
== How do I make Octave use more precision? ==
 
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 a few other built-in types. The int64 type will have 63 bits of precision. One bit is used for the sign, but if you don't want to lose that bit, uint64 can be used instead. These types, however, cannot represent numbers as large as the default double type, and can only represent integers. Furthermore, there is no way to represent integer literals, so if you do
 
<syntaxhighlight lang="Octave">uint64(18446744073709551610);</syntaxhighlight>
 
the literal "18446744073709551610" first gets converted to a double precision type, so <code>uint64</code>'s additional precision is lost. Alternatively, the symbolic package, when it works, has a vpa() function for variable-precision arithmetic. Note that arbitrary-precision arithmetic is implemented '''in software''' which makes it much slower than hardware floats.
 
At present, however, the symbolic package is almost useless, since even when you get it to compile and not crash, it cannot handle any array type, which hardly helps for an array-oriented language like Octave. If this limitation is not important to you, attempt to use the symbolic package. If you would like to get this fixed, [http://octave.1599824.n4.nabble.com/Internal-Precision-Symbolic-tp4645257p4645594.html Jordi Gutiérrez Hermoso has volunteered] to fix the package for 5000 USD, which can be obtained from a kickstarter compaign.
 
Consider carefully if your problem really needs more precision. Often if you're running out of precision the problem lies fundamentally in your methods being [http://en.wikipedia.org/wiki/Numerical_stability numerically unstable], so more precision will not help you here. If you absolutely must use arbitrary-precision arithmetic, you're at present better off using a CAS instead of Octave. An example of such a CAS is [http://sagemath.org Sage].
 
=Common problems=
 
==When I try plotting from a script, why am I not seeing anything?==
 
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.
 
A common solution is to put a {{Codeline|pause}} command at the end of your script.
 
==How do I get sound output in Windows?==
See http://www.octave.org/octave-lists/archive/help-octave.2003/msg01567.html for a start.
 
==Why does Octave segfault when using "clear all;"?==
 
This is a known problem if you have one of the following packages loaded:
 
* ann
* database
* ftp
 
See http://www.nabble.com/Segmentation-Fault---Clear-all-td21998563.html for a discussion
 
==Octave takes a long time to find symbols.==
 
Octave uses the genpath function to recursively add directories to the list of directories searched for function files. Check the list of directories with the path command. If the path list is very long check your use of the genpath function.
 
==When plotting Octave occasionally gives me errors like <tt>gnuplot> 9 0.735604 line 26317: invalid command</tt>.==
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 4.4.
 
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 included.
 
==I cannot install a package. Octave complains about a missing mkoctfile.==
 
Most distributions split Octave into several packages. The script mkoctfile is then part of a separate package:
 
* Debian/Ubuntu: {{Codeline|octave-headers}} or {{Codeline|liboctave-dev}}
 
* Fedora: {{Codeline|octave-devel}}
 
== I'm having problem XXX using the latest Octave version ==
 
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 get Octave, and 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]]).
 
If you mean the latest Mercurial revision, please specify which one that is. "Latest tip" is not informative, because from the time you wrote "latest tip" to the time someone reads that message, "latest tip" might have changed meaning. Instead, report the output of "hg summary" or "hg id". Also please use hash numbers instead of 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.
 
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 be surprised if volunteers are less inclined to help you with a problem that only exists in an older version of Octave.
 
== Why is this floating point computation wrong? ==
 
Floating point arithmetic is an approximation '''in binary''' to arithmetic on real or complex numbers. Just like you cannot represent 1/3 exactly in decimal arithmetic (0.333333 is only a rough approximation to 1/3), you cannot represent some decimals like 0.1 exactly in base 2. In binary, the representation to one tenth is <math>0.\overline{00011}</math> where the bar indicates that it repeats infinitely (like how <math>1/3 = 0.\overline{3}</math> 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 - 0.2 - 0.1 is not equal to zero.
 
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]. The reason why Octave and other programs use IEEE 754 floats is that they are ''fast'', because they are implemented in hardware. Unless you are using very exotic hardware, Octave will use your computer's processor for floating point arithmetic.
 
Like death and taxes, rounding errors are a fact of life. You cannot avoid them. You can only move a rounding error from one part of a computation to another, or you can use more precision and delay the rounding error. One way to delay the rounding error is to use arbitrary precision arithmetic, which is inevitably slower as it has to be implemented in software instead of hardware. You may use the vpa function from the symbolic package for this purpose.
 
To learn more about floating point arithmetic, consult [http://en.wikipedia.org/wiki/Floating_point_arithmetic its Wikipedia article] or the classical reference [http://floating-point-gui.de/ What Every Computer Scientist Should Know About Floating Point Arithmetic].
 
== I have installed a package but still get a "foo undefined" error ==
 
You have probably forgotten to load the package. Use {{Codeline|pkg load package-name}} to load it. Most packages are no longer loaded automatically to avoid surprises. See reasoning on related FAQ [[FAQ#How_do_I_install_all_Octave_packages.3F|how do I install all Octave packages]]. If you want a specific package to be loaded by default at startup, consider adding the {{Codeline|pkg load}} command on your {{path|.octaverc}} file.
 
=Porting programs from Matlab to Octave=
 
People often ask
 
<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>
 
or alternatively
 
<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. 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 the page http://octave.sourceforge.net/packages.html and http://octave.sourceforge.net/doc/ that has a function reference that is up to date. You can use this function reference to see the number of octave function that are available and their Matlab compatibility.
 
==How is Octave different from Matlab?==
 
The major differences between Octave 3.4.N and Matlab R2010b are:
 
===Nested Functions===
Octave has limited support for nested functions. That is
 
          function y = foo (x)
            y = bar(x)
            function y = bar (x)
              y = ...;
            end
          end
 
is equivalent to
 
          function y = foo (x)
            y = bar(x)
          end
          function y = bar (x)
            y = ...;
          end
 
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 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 supported, though work is underway in a branch of the development tree.
 
===Differences in core functions===
 
A large number of the Matlab core functions (ie 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 sprandn function can not force a particular condition number for the matrix like Matlab can.
 
===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 a JIT and so to some might seem slower than Matlab. For this reason you must 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 support for graphics handles is converging towards full compatibility. The patch function is currently limited to 2-D patches, due to an underlying limitation in gnuplot, but the experimental OpenGL backend is starting to see an implementation of 3-D patches.
 
===GUI functions ===
 
There are no Matlab compatible GUI functions yet.  This might be an issue if you intend to exchange Octave code with Matlab users. There are a number of bindings from Octave to {{Forge|tcl-octave|Tcl/Tk}}, [http://octaviz.sourceforge.net/index.php? VTK] 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.
 
===Simulink===
 
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 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===
 
Block comments denoted by {{Codeline|#{}} and {{Codeline|#&#125;}}  markers (or {{Codeline|%{}} and {{Codeline|%&#125;}}) 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, 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.


<syntaxhighlight lang="octave">
===Short-circuit {{Codeline|&}} and {{Codeline|&#124;}} operators===
>> exist ("foo.txt", "file")  # 2, if file exists, 0 otherwise
ans = 2
</syntaxhighlight>


==How do I create a plot without a window popping up (plot to a file directly)?==
The {{Codeline|&}} and {{Codeline|&#124;}} 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|&&}} and {{Codeline|&#124;&#124;}} short circuit. Note that this means that


<syntaxhighlight lang="octave">
            if (a | b)
figure (1, "visible", "off");
              ...
plot (sin (1:100));
            end
print -deps "/tmp/sin.eps"
</syntaxhighlight>


One can set that behavior as default:
and


<syntaxhighlight lang="octave">
            t = a | b;
set (0, "defaultfigurevisible", "off");
            if t
</syntaxhighlight>
              ...
            end


==How do I increase Octave's precision?==
have different semantics in Matlab. This is really a Matlab bug, but there is too much code out there that relies on this behaviour to change it. Prefer the {{Codeline|&#124;&#124;}} and {{Codeline|&&}} operators in {{Codeline|if}} statements if possible. If you need to use code written for Matlab that depends on this buggy behaviour, you can enable it since Octave 3.4.0 with the following command:


Octave's default numerical type is [https://en.wikipedia.org/wiki/IEEE_754 IEEE 754] binary64, a.k.a. "double" or "hardware floats".  This type has a precision of 53 bits or about 16 decimal digits. It is supported by each modern computer hardware, so it is really '''fast'''.  This type is assumed throughout for Octave's calculations.  If more precision was required, one can obtain a "few bits more" by using integer types, e.g. {{manual|uint64}}, but in general one cannot expect more precision from any '''fast''' numerical software.  Just to visualize "how big" those numerical limits are, consider the following table:
            do_braindead_shortcircuit_evaluation(1)


{| class="wikitable"
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
|+ 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")</code>
| style="text-align: right;" | <code>9,007,199,254,740,992</code>
| <code>2^53</code>
|-
| <code>flintmax ("single")</code>
| style="text-align: right;" | <code>16,777,216</code>
| <code>2^24</code>
|}


When working with other types than "double" in Octave, one has to make sure, that the first operand is converted to the desired type:
            t = 1 | [];          ## results in [], so...
            if (t) 1, end        ## in if ([]), this is false.


<syntaxhighlight lang="Octave">
and
>> uint64 (2^53 + 1)
ans = 9007199254740992
>> uint64 (2^53) + 1
ans = 9007199254740993
</syntaxhighlight>


Notice the difference, in the first line the addition within the brackets is performed using double precision, therefore the result gets "truncated" to the maximum possible value without a warning.  The third line uses throughout uint64 precision.
            if (1 | []) 1, end  ## short circuits so condition is true.


Consider carefully if your problem really needs more precision.  Often if you're running out of precision the problem lies fundamentally in your methods being [https://en.wikipedia.org/wiki/Numerical_stability numerically unstable], thus more precision will not help you here.
Another case that is documented in the Matlab manuals is that


If you absolutely must have more precision, you're at present better off using a [https://en.wikipedia.org/wiki/Computer_algebra_system CAS] instead of Octave.  However, CAS or symbolic computations must be implemented '''in software''' which 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]].
            t = [1, 1] | [1, 2, 3];          ## error
            if ([1, 1] | [1, 2, 3]) 1, end  ## OK


==How do I run a Matlab P-file in Octave?==
Also Matlab requires the operands of {{Codeline|&&}} and {{Codeline|&#124;&#124;}} 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).


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 that cannot be run outside of Matlab itself.  The original source Matlab m-files that were used to generate these P-files should be used in Octave instead.
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:


There are no plans to support running P-files produced by Matlab in Octave.
            if ([0, 1]) == if (all ([0, 1]))  ==>  i.e., condition is false.
            if ([1, 1]) == if (all ([1, 1]))  ==>  i.e., condition is true.


==How does Octave solve linear systems?==
However,
 
            if ([])
 
is not the same as
 
            if (all ([]))
 
because, despite the name, the {{Codeline|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 [http://en.wikipedia.org/wiki/Vacuous_truth vacuous truth]. But, somewhere along the line, someone decided that {{Codeline|if ([])}} should be false. 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 mldivide (\) and mrdivide (/), 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


In addition to consulting Octave's source for the precise details, you can read 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 <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.
          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


==How do I do X?==
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.


You are probably looking for the function {{manual|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 <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:
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:


  >> lookfor correlation
          m = 10;
  corr                Compute matrix of correlation coefficients.
          n = 10000;
  corrcoef            Compute a matrix of correlation coefficients.
          A = ones(m, n) + 1e-6 * randn(m,n);
  spearman            Compute Spearman's rank correlation coefficient RHO.
          b = ones(m, 1) + 1e-6 * randn(m,1);
          norm(A \ b)


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 <code>corr</code> at the octave prompt followed by pressing the {{key press|Tab}}-Key twice would suggest the following:
while Octave's minimum-norm values are around 3e-2, Matlab's results are 50-times larger. For another issue, try this code:


  >> corr
          m = 5;
  corr    corrcoef
          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)


=Differences between Octave and Matlab=
It shows that unlike in Octave, 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.
:''See [[Differences between Octave and Matlab]]''.


=[https://en.wikipedia.org/wiki/Graphical_user_interface GUI]=
Since the mldivide (\) and mrdivide (/) 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.


==Does Octave have a GUI?==
===Octave extensions===


'''Yes!''' It was officially released with Octave 4.0.0.  It was also available since version 3.8.0 as an experimental feature (use the {{Codeline|--force-gui}} option to start Octave).
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:


==Why did you create yet another GUI instead of making one that already exists better?==
Comments in octave can be marked with {{Codeline|#}}. This allows POSIX systems to have the first line as {{Codeline|#! octave -q}} and mark the script itself executable. Matlab doesn't have this feature due to the absence of comments starting with {{Codeline|#}}".


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:
Code blocks like if, for, while, etc can be terminated with block specific terminations like endif. Matlab doesn't have this and all blocks must be terminated with end.


* '''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.
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.


* '''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 a separate project.  Also, many bits from QtOctave were reused in the GUI.
Note that using try/catch combined with {{Codeline|rethrow (lasterror ())}} can not guarantee that global variables will be correctly reset, as it won't catch user interrupts with Ctrl-C. For example


* '''[http://www.xoctave.com/ Xoctave]''', which is proprietary and commercial.
                global a
                a = 1;
                try
                  _a = a;
                  a = 2
                  while true
                  end
                catch
                  fprintf ('caught interrupt\n');
                  a = _a;
                  rethrow (lasterror());
                end


* '''GUI Octave''', which was proprietary and is no longer available.
compared to


=Graphics: backends and toolkits=
                global a
                a = 1;
                unwind_protect
                  _a = a;
                  a = 2
                  while true
                  end
                unwind_protect_cleanup
                  fprintf ('caught interrupt\n');
                  a = _a;
                end


==What are the supported graphics backends?==
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.


* [https://www.opengl.org/ OpenGL] via the graphics toolkits '''[https://www.qt.io/ qt]''' (current default) and '''[http://www.fltk.org/ fltk]'''
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]);}}
* [http://www.gnuplot.info/ gnuplot] via the '''gnuplot''' graphics toolkit


==How do I change my graphics toolkit?==
Octave has the operators {{Codeline|++}}, {{Codeline|–}}, {{Codeline|-&#61;}}, {{Codeline|+&#61;}}, {{Codeline|*&#61;}}, etc. As Matlab doesn't, if you are sharing code these should be avoided.


There are three commands to deal with graphics toolkits:
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.


{| class="wikitable"
=GUI=
| <code>available_graphics_toolkits</code>
This is a small section but it's probably one of the most frequent questions.
| lists all available graphics toolkits
|-
| <code>graphics_toolkit</code>
| displays the currently used graphics toolkit
|-
| <code>graphics_toolkit ("qt/fltk/gnuplot")</code>
| sets the graphics toolkit to 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 with an OpenGL backend?==
==Is there a GUI for Octave?==
No.


The development of Octave is committed to being both compatible with Matlab and adding additional features.  Toward those ends, the 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).
==Is there a GUI planned for Octave?==
Yes, and is already in development. You can download the [http://www.gnu.org/software/octave/get-involved.html Octave repository] and compile the development branch yourself (it seems to be stable enough for use and the 3.6.2 binaries for windows already have it). Testing is always welcomed, and patches even more. Note that despite being called Octave GUI, it is ''not'' a separate project. It is simply the ''Octave GUI'', the Octave Graphical User Interface, just like the Octave prompt, Octave interpreter, etc are not separate projects (not to be confused with the completely unrelated but similarly named, GUI Octave project).


==Are there any plans to remove the gnuplot backend?==
==How come there's still no GUI for Octave?==
The Octave prompt is really really good and that's what the Octave developers use. Octave is community project which means that it has the functionalities that its users are willing to spend time implementing. Since Octave developers do not need a GUI (some actually would not use one if it existed), they have no reason to make one. Also, many people on the community are of the opinion that using a GUI slows down the learning of the language.


'''No.''' There are no plans to remove the gnuplot backend. It will be available as long as our users find it useful.
==I want Octave developers to work on a GUI?==
If you would like the Octave developers to implement a GUI for you, consider the same route taken by others that want a specific function/capability to be implemented. Some of the Octave developers will work as coders for hire. Ask on the [http://www.gnu.org/software/octave/get-involved.html maintainers mailing list]. This is not unlike paying a builder to add an extra room to your house. The fact there is no GUI in Octave only shows that there is not enough interest for it (despite the amount of time people asking for it).


==How can I implement a new graphics backend/toolkit?==
==What about all the Octave GUIs I find on Google?==
None of the GUIs for Octave that have been developed thus far are part of Octave and there is a reason for it. All of them fail at a very important point, integration with Octave. They treat Octave as a foreign black box using pipes for communication, an approach that is bound to eventually fail. This includes QtOctave (now abandoned and incompatible with newer versions of Octave), Xoctave (which is proprietary and commercial) and GUI Octave (which is proprietary and the author is not interested to share his code to preserve its "artistic integrity").


This is one of those times where the best documentation is to read the existing code.  We have three different toolkits in Octave now, so there are some examples to draw from.
Quint was a project for an Octave GUI that actually tried to do it right. Eventually it was merged into the Octave repository and is now under development under the name Octave GUI (this is not a separate project anymore, it is simply the ''Octave GUI'' and not to be confused with the completely unrelated but similarly-named, GUI Octave project).


= Development =
==QtOctave has been abandoned. Why are you working on yet another GUI rather than trying to fix QtOctave?==
Read previous question. The approach taken by QtOctave for interacting with Octave is bound to fail. Yes, it could be fixed and made to work again for the latest octave release but this would not be a permanent fix and would eventually fail again. A [http://octave-gsoc2012.blogspot.ie/2012/06/why-not-take-existing-gui.html longer explanation] has already been written as part of GSoC2012.


== When will feature X be released or implemented? ==
Yes, QtOctave is a useful tool, looks beautiful and we are thankful to its developers for working on such a nice tool plus making it libre. We are in no way saying the opposite. However, it will ''never'' be stable. The Octave GUI being developed now uses code from many different projects, we are trying to not reinvent the wheel. But we want something that will achieve stability.


When it's ready, sooner [https://www.octave.org/get-involved.html if you help].  You can [https://savannah.gnu.org/patch/?group=octave send us patches] if you can implement feature X yourself. If you can't, some [https://www.octave.org/commercial-support.html developers may be convinced to work on your specific problem for some money].
==What about GUI Octave?==
GUI Octave is not part of the Octave project despite its very deceptive name. Not only is a different project, it is also very inappropriate for this piece of closed-source software to occupy the name "GUI Octave" with the hostile anti free-software stance the developer has taken. It advertises itself as a "completely free" wrapper to "GNU Octave". It must be explicit that it is not free software as understood by GNU. This is deceptive.


== How can I get involved in Octave development? ==
==How can I know more about Octave GUI?==
This is being developed as part of the Octave project so subscribe to the [http://www.gnu.org/software/octave/get-involved.html maintainers mailing list]. When you checkout the Octave repository, you'll find the GUI source on the development/default [http://hg.savannah.gnu.org/hgweb/octave/branches branch].


:''See [[Developer FAQ]]''.
You may also read [http://octave-gsoc2012.blogspot.ca/ Jacob's blog posts about the topic.]


[[Category:FAQ]]
==I'm having problem XXX using GUI Octave, XOctave, QtOctave, etc?==
Install Octave only, without any of the non-supported by GUIs and see if the problem disappears.
Please note that all contributions to Octave may be edited, altered, or removed by other contributors. If you do not want your writing to be edited mercilessly, then do not submit it here.
You are also promising us that you wrote this yourself, or copied it from a public domain or similar free resource (see Octave:Copyrights for details). Do not submit copyrighted work without permission!

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