# Changes

## FAQ

, 13 June
m
This is a list of frequently asked questions (FAQ) for GNU Octave users.
We are always looking for new questions (with answers), better answers, or both. Feel free to edit this page with your changes. If you have general questions about GNU Octave, or need help for something that is not covered by the Octave manual or the FAQ, please use the [https://lists.gnu.org/mailman/listinfo/help-octave help@octave.org mailing list].
This =Where do I get additional help?= If you can't find an answer to your question in this FAQ is intended to supplement, not replacewiki, or in the GNU Octave manual ([httpshttp://www.gnuoctave.org/software/octave/doc/interpreter/ HTMLmanual], ([httpshttp://www.gnuoctave.org/software/octave/octave.pdf PDF])you can: * Search for an answer in our [https://lists.gnu. Before posting a question to the org/archive/html/help-octave/ mailing list archives]* Contact our user community using our [https://lists.gnu.org/mailman/listinfo/help-octave help@octave.org mailing list], you should first check (feel free to subscribe to see if the topic is covered this mailing list)* Contact our user community using our [https://webchat.freenode.net/?channels=octave IRC chat room <code>#octave</code> in the manual.Freenode]
<div class="tocinline">__TOC__</div>
[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.
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.
==What is Octave-Forge?==
[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).
==Who uses Octave?==
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 fund. However, Octave is not and has never been developed by the FSF.
==What version should I use?== 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/. The used version of Octave is available via the <code>ver</code> command and a list of user-visible changes since the last release is available via the <code>news</code> command at the GNU Octave prompt. ==On what platforms does Octave run?== 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]. == 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 used. To cite GNU Octave in publications use:
John W. Eaton, David Bateman, Søren Hauberg, Rik Wehbring (2017{{Release Year}}).
GNU Octave version {{Release}} manual: a high-level interactive language for numerical computations.
URL https://www.gnu.org/software/octave/doc/v{{Release}}/
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},
year = <span>{2017</span>{{Release Year}}},
url = {https://www.gnu.org/software/octave/doc/v{{Release}}/},
}
Run <code>{{manual|citation</code> }} 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>.
Note that there are two reasons for citing the software used. One is giving recognition to the work done by others which we already addressed. 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. 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.
==When will feature X be released or implementedWhat documentation exists for Octave?==
When it's readyBesides this wiki, sooner the GNU Octave distribution includes a [http://www.octave.org/get-involved.html if you help]. You can [https:/doc/savannah.gnu.org/patch/?group=octave send us patchesinterpreter 1000+ page Texinfo manual] if you can implement feature X yourself. If you can't, some ([http://www.octave.org/commercial-support.html developers may be convinced to work on your specific problem for some money]. ==How can I get involved in Octave development?== Be around. Be social. Participate in our mailing lists [https://lists.gnu.org/mailman/listinfo/help-octave help@octave.org] and [https://lists.gnu.org/mailman/listinfo/octave-maintainers maintainers@octave.orgpdf PDF]). Find things about Octave you don't like, and start thinking about how Access 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 complete text of the manual is available via the {{manual|doc}} command at the codeGNU Octave prompt. A good way to learn Octave is to understand the If you have problems other people are having with itusing this manual, so being helpful in the mailing lists or find that some topic is not only helps Octave as a wholeadequately explained, indexed, or cross-referenced, but please report it also prepares you to be a better Octave contributoron http://bugs.octave.org.
If you feel ready to dive right into the code, read the [[Developers]] wiki page or [http://www.octave.org/get-involved.html start here]. But do not send an email to the mailing lists listing your skills and offering to help. We won't just suggest things for you to do. We lack volunteers and we do need your help, but because of that, we also lack the time to provide good guidance and mentoring. If there is ==How can I report a specific short-term project you would like to work on, say so, and just do it. Then ask for help or advice when you're doing it. It is a lot more important that you do something that you're actually interested on than something we suggested because it only matches your skills.bug in Octave?==
We also need help with this wiki and the [Please read our website http://www.octave.org/doc/interpreter/ manual]. These are also important tasks. The documentation is easy to patch, and the help text for individual functions even more so. Editing this wiki is even easier. Accurate bug reporting is also very useful. Find and report [http://bugs.octave.org/ bugs], making an attempt to diagnose them. Eventually, you will also know how to fix them. If you want to help with bug reports or patches, subscribe to the [https://lists.gnu.org/mailman/listinfo/octave-bug-tracker bug tracker mailing list]. You'll get updates on all bug activity, and you can jump in when you seesomething you can help withLook at our [[projects]], [[short projects]], and [[Summer of Code Project Ideas]] if you need specific inspiration for coding tasks that we would like to get donehtml.
=Licensing issues=
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]].
Each new ==On what platforms does Octave release introduces many new features. A complete list of user visible changes can be seen by running {{codeline|news}} at the Octave prompt. The following changes are a distilled list of the major changes:run?==
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]. ==Coming How can I obtain Octave's source code?== The latest version of the Octave source code (and older versions) is available from: * https://www.octave.org/download.html* 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. ==How can I build Octave from the source code?== 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]]. If you have reasons to build Octave from the source code, see [[Building]] for more information. ==What do I need to build Octave from the source code?== For a list of build dependencies see [[Building]]. ==Do I need GCC to build Octave from the source code?== No. The development is done primarily with [https://gcc.gnu.org/ GCC], so you may hit some incompatibilities. Octave is intended to be portable to any standard conforming compiler (for example [https://clang.llvm.org/ clang] is know to work as well). If you have difficulties that you think are bugs, please report them to the [http://bugs.octave.org bug tracker], or ask for help on the [https://lists.gnu.org/mailman/listinfo/help-octave help@octave.org mailing list]. =What's new in Octave?= 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. The following changes are a future releasedistilled list of the major changes: ==What's new in the next version of Octave?==
See the [http://hg.savannah.gnu.org/hgweb/octave/file/tip/NEWS NEWS file] on the development branch.
* Many improvements to native OpenGL plotting
* ARPACK now distributed with Octave
* Indexing optimisationsoptimizations
* FTP objects
* Function handles aware of overloaded functions
* bsxfun optimised optimized for basic arithmetic functions
* Matlab-style ignoring of output arguments using {{Codeline|~}}
* Many optimisations optimizations of the accumarray function
* Sparse matrix indexing has been rewritten for speed
* The pkg command now accepts a -forge option to pull packages directly from Octave-forgeForge
==What's new in version series 3.2.X of Octave==
* a fully compatible MEX interface
* imwrite and imread (based on the GraphicsMagick library)
* Lazy transpose <br/> : Special treatment in the parser of things like "a' * b", where the transpose is never explicitly formed but a flag is rather passed to the underlying LAPACK code.
== Older releases ==
For full details on older releases, see:
* [http://hg.savannah.gnu.org/hgweb/octave/file/83792dd9bcc1/etc/NEWS.3 NEWS.3] for the 3.X.Y series
=What documentation exists for Packages and Octave?Forge=
Besides this wiki, 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 ==How do I install or load all 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.Forge packages?==
==Getting additional help==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 caseyou know them by name; or you want them all "just because", in which case you don't really need them.
If you can't find an answer to your questionThe common misconception is that the more packages one has installed and loaded, the help@octavemore complete and powerful its Octave installation will be.org mailing list is available for questions related to using However, in the same way one would never install all perl modules, ruby gems, installingpython packages, and porting Octave that are C++ libraries (because it simply makes no sense), one should not adequately answered by the install all Octave manual or by this documentpackages.
==User community==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 subscribe If you really really really want to do load all packages, you can with the list, go to httpfollowing://www.<syntaxhighlight lang="octave">## WARNING: loading all packages is probably not the solution you are looking for.org/archivecellfun (@(x) pkg ("load", x.html and follow the link to the subscription page for the name), pkg ("list."));</syntaxhighlight>
Please do not send requests to be added or removed from the mailing list, or other administrative trivia to the list itself.==I have installed a package but still get a "foo undefined" error?==
An archive of old postings You have probably forgotten to load the helppackage. Use {{Codeline|pkg load package-octave mailing list is maintained name}} to load it. Most packages are no longer loaded automatically to avoid surprises. See reasoning on http://wwwrelated FAQ [[FAQ#How_do_I_install_all_Octave_packages.octave3F|how do I install all Octave packages]].org/archive If you want a specific package to be loaded by default at startup, consider adding the {{Codeline|pkg load}} command on your {{path|[[.htmloctaverc]]}} file.
You will also find some user advice and code spread over the web==I cannot install a package. Good starting points are the Octave Wiki http://wikicomplains about a missing mkoctfile.octave.org and Octave-Forge http://octave.sourceforge.net==
We also have [http: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</webchat.freenode.net?channels=octave&uio=d4 an IRC chat room]code>, and you should install that instead using <code>#octaveapt</code> or <code>yum</code> in Freenode.
==I think I have found a bug in If you really need to build Octave packages from source to install them, you'll need {{manual|mkoctfile}}. Most distributions split Octaveinto several packages.== The script {{manual|mkoctfile}} is then part of a separate package:
“I think I have found a bug in Octave, but I'm not sure* Debian/Ubuntu: [https://packages. How do I know, and who should I tell?”debian.org/stretch/liboctave-dev liboctave-dev]
Yes, but development is done primarily with GCC, so you may hit some incompatibilities. ==How do I automatically load a package at 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].startup?==
== How do install or 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 all Octave packages? ==pkg-name</code> command to it. If the files does not exist, create it.
Do not If you do it! Reallythis, there is no reason remember that other people may not have Octave configured to do this. Octave has manyload packages for different needs and is unlikely that you need all ofthemat startup. You either have a small set of required packagesTherefore, in which caseif you know them by name; or you want them all "just because"write code for others, in which caseyou don't really remember that your programs still need themto load the packages they require.
==How do I execute an Octave script?==
First of all, make sure you understand [http://www.gnuoctave.org/software/octave/doc/interpreter/Script-Files.html the difference between script files and function files]. If you want to execute a function defined in a file, just call the function like any other Octave function: <code>foo(arg1, arg2);</code>
To execute a script from within Octave, just type its name without the <code>.m </code> extension. Thus, if you have a script called <code>foo.m</code>, just type <code>foo</code> from within the Octave command prompt to execute it. You have to make sure that the script is in your current working directory or in Octave's load path. Type <code>path</code> in Octave to see what this path is, and type <code>{{manual|pwd</code> }} to print get the current working directory (where youor type {{manual|path}} to see which paths belong to Octave're currently standing)s load path. The current working directory is referred to as "." in the <code>output of {{manual|path</code>}}.
If the script name has characters that are not valid for an Octave identifier, or if you do not want to use {{manual|addpath }} to add the script's location to the current path, you can use the <code>{{manual|run</code> }} function instead:
<syntaxhighlight lang="octave"> run("Script Name With Spaces.m") octave> run("/opt/local/foo.m")</syntaxhighlight>
An alternative is to run the script from outside Octave by calling Octave from your operating system shell. Unlike calling the script from inside Octave, this also allows you to pass arguments from the shell into the script, which the script can access using the <code>{{manual|argv</code> }} command:
\$ octave the-script.m arg1 arg2
If you call the script from the shell and it's plotting, please note [[#When I try plotting from a script, why am I not seeing anything?|how to plot when running a script from the shell]].
==How do xxxxI close a figure?==
You are probably looking for To close the function ''lookfor''. This function searches the help text of all functions for a specific string and returns a list of functions. Note that by default it will only search the first line of the help text (check ''help lookfor'' at current figure type {{manual|close}} in the octave Octave command prompt for more). The following example helps to find the function to calculate correlation coefficient in a matrix:
octave> lookfor correlation corr2 Returns the correlation coefficient between ==How do I and J. cor Compute correlation. corrcoef Compute correlation. spearman Compute Spearman's rank correlation coefficient RHO for each of the variables sp autocor Return set the autocorrelations from lag 0 to H number of vector X. Also, there's a high chance that the function name has a suggestive name, and so you can try auto-completion to get some hints. For the previous example, typing ''corr'' at the octave promp followed by pressing [Tab] twice would suggest the following:displayed decimals?==
octave> corr corr2 corrcoef ==How do I erase a figure?==   closeplot(); closefig(number) ==How do I set You can control the number of displayed decimals?==using the {{manual|format}} command:
<syntaxhighlight lang="octave:1">>> format long octave:2>> pi pi = 3.14159265358979 octave:3>> format short octave:4>> pi pi = 3.1416</syntaxhighlight>
==How do I call an octave Octave function from C++?==
*Here is an untested code snippet for calling rand([9000,1]), modified from a post by HerberFarnsworth? to helpPlease read the manual https://www.gnu.org/software/octave/doc/interpreter/Calling-Octave-octave on 2003Functions-05from-01: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) How do I change color/line definition in gnuplot postscript?= octave_value(NumRands); f_ret = feval("rand",f_arg,1); Matrix unis(f_ret(0).matrix_value());
==How do I change colour/line definition in gnuplot postscript?==Here is a awk script to get a rainbow colour color map
#!/bin/awk -f
==How do I tell if a file exists?==
Look at functions like One can use the function {{manual|exist}} to tell if a regular file, file_in_pathsay <code>foo.. and txt</code> exist in Octave's load path, or the other functions that their descriptions point to.current directory:
<syntaxhighlight lang="octave">
>> exist ("foo.txt", "file") # 2, if file exists, 0 otherwise
ans = 2
</syntaxhighlight>
==How do I create a plot without a window popping up (ie, a plot to a filedirectly)?==
'''This only works with gnuplot as graphics_toolkit<syntaxhighlight lang="octave">figure (1, NOT with fltk. See [https"visible", "off");plot (sin (1:100));print -deps "/tmp/savannah.gnusin.org/bugseps"</?33180 Bug#33180]'''syntaxhighlight>
figure(1, "visible", "off"); plot(sin(1One can set that behavior as default:100)); print -deps "/tmp/sin.eps"
One can <syntaxhighlight lang="octave">set that behaviour as default:(0, "defaultfigurevisible", "off");</syntaxhighlight>
set(0, ==How do I increase Octave'defaultfigurevisible', 'off');s precision?==
== How do I make Octave use '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:
{| class="wikitable"|+ Limits of some of Octave's default numerical type is IEEE 754 doublesdata types obtained by {{manual|intmax}} and {{manual|flintmax}}.|-| <code>intmax ("uint64")</code>| style="text-align: right;" | <code>18,446, a.k.a. hardware floats. This type has 52 bits of precision or about 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 decimal digits. It's implemented in your computer's hardware, in your CPU777, so it's '''fast'''. This type is assumed throughout for Octave's calculations.216</code>| <code>2^24</code>|}
You can use a few When working with other built-types than "double" in types. The int64 type will have 63 bits of precision. One bit is used for the signOctave, but if you don't want one has to lose make sure, 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 first operand is no way converted to represent integer literals, so if you do the desired type:
<syntaxhighlight lang="Octave">>>uint64(184467440737095516102^53 + 1);ans = 9007199254740992>> uint64 (2^53) + 1ans = 9007199254740993</syntaxhighlight>
Notice the difference, in the literal "18446744073709551610" first gets converted to a line the addition within the brackets is performed using double precision type, so <code>uint64</code>'s additional precision is lost. Instead, initialise therefore the <code>uint64</code> with smaller numbers and perform a computation result gets "truncated" to get the larger number you wantmaximum possible value without a warning. E The third line uses throughout uint64 precision.g.,
<syntaxhighlight lang="Octave">uint64(999999999999999) * 10000<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:/syntaxhighlight>/en.wikipedia.org/wiki/Numerical_stability numerically unstable], thus more precision will not help you here.
would produce value 9999999999999990000If you absolutely must have more precision, which is close to the maximum possible value for the uint64 type, but canyou't be re at the moment input directly, doing uint64(9999999999999990000), due to the mentioned error present better off using a [https://en.wikipedia.org/wiki/Computer_algebra_system CAS] instead of roundingOctaveAlternatively However, one may use arbitrary precision arithmetic, which has as much precision as is practical to hold in your computer's memory. The ''CAS or symbolic'' package has a vpa() function for arbitrary precision arithmetic. Note that arbitrary precision arithmetic computations must be implemented '''in software''' which makes it much slower than hardware floats. 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://www.sagemath.org / Sage] or have a look at Octave's [[Symbolic package]].
==How do I run a Matlab P-file in Octave?==
You can't. Matlab P-files (files with a <code>.p </code> file extension), also known as P-code, are [https://en.wikipedia.org/wiki/Obfuscation_%28software%29 obfuscated] files than cannot be run outside of Matlab itself. The original source Matlab m-files that were used to generate the these P-files should be used in Octave instead.
There are no plans to support running P-files produced by Matlab in Octave.
=Common problems=How does Octave solve linear systems?==
==I am running In addition to consulting Octave's source for the precise details, you can read the Octave manual for a script complete high-level description of the algorithm that should produce output during execution but I don't see anything until it has finished==Octave uses to decide how to solve a particular linear system, e.g. how the backslash operator <code>A \ x</code> will be interpreted. Sections [http://www.octave.org/doc/interpreter/Techniques-Used-for-Linear-Algebra.html Techniques Used for Linear Algebra] and [http://www.octave.org/doc/interpreter/Sparse-Linear-Algebra.html Linear Algebra on Sparse Matrices] from the manual describe this procedure.
By default Octave is set to pass its screen output through a pager (usually the default pager is "less") which allowsthings such as navigating through the output with arrow keys or searching for text or regular expressions within the output.The pager only displays the output after it's finished receiving it, so when it is active you'll not be able to see anything until your script has terminated. To change this behavior temporarily or permanently you may want to use one of the options described [http://www.gnu.org/software/octave/doc/interpreter/Paging-Screen-Output.html here].==How do I do X?==
==When I try plotting from You are probably looking for the function {{manual|lookfor}}. This function searches the help text of all functions for a script, why am I not seeing anything?==specific string and returns a list of functions. Note that by default it will only search the first line of the help text (check <code>help lookfor</code> at the octave prompt for more). The following example helps to find the function to calculate correlation coefficient in a matrix:
If you are running an Octave script that includes >> lookfor correlation corr Compute matrix of correlation coefficients. corrcoef Compute a plotting command, the script and Octave may terminate immediatelymatrix of correlation coefficients. So the plot window does show up, but immediately closes when Octave finishes execution. Alternatively, if using fltk, the plot window needs a readline loop to show up (the time when Octave is sitting around doing nothing waiting for interactive input) spearman Compute Spearman's rank correlation coefficient RHO.
A common solution is Also, there's a high chance that the function name has a suggestive name, and so you can try auto-completion to put a get some hints. For the previous example, typing <code>corr</code> at the octave prompt followed by pressing the {{Codelinekey press|pauseTab}} command at -Key twice would suggest the end of your script.following:
==How do I get sound input or output in Windows?== >> corrSound input from a sound card and output to a sound card is fully supported in Octave 4.0.0 and newer in all operating systems. Older versions of Octave had very limited audio support that was essentially Linux-specific. If you have problems with the audio I/O functions using Octave 4.0 or a newer version, please report them on the [http://bugs.octave.org bug tracker]. corr corrcoef
==I cannot install a package. Octave complains about a missing mkoctfile.=Common problems=
You should normally use your distribution's packages. For Debian and Fedora, Octave package '''foo''' will be a deb or rpm called '''octave-foo''', and you should install that instead using apt or yum.==I do not see any output of my script until it has finished?==
If you really need to build By default Octave packages from source is set to install thempass its screen output through a [https://en.wikipedia.org/wiki/Terminal_pager pager] (usually the default pager is "less") which allows things such as navigating through the output with arrow keys or searching for text or regular expressions within the output. The pager only displays the output after it's finished receiving it, so when it is active you'll need mkoctfilenot be able to see anything until your script has terminated. Most distributions split Octave into several packages. The script mkoctfile is then part To change this behavior temporarily or permanently you may want to use one of a separate packagethe options described [http://www.octave.org/doc/interpreter/Paging-Screen-Output.html in the manual].
* Debian/Ubuntu: {{Codeline|octave-headers}} or {{Codeline|liboctave-dev}}==When I try plotting from a script, why am I not seeing anything?==
* Fedora: {{Codeline|octave-devel}}If you are running an Octave script that includes a plotting command, the script and Octave may terminate immediately. So the plot window does show up, but immediately closes when Octave finishes execution. Alternatively, if using fltk, the plot window needs a readline loop to show up (the time when Octave is sitting around doing nothing waiting for interactive input).
== I'm having problem XXX using A common solution is to put a {{manual|pause}} command at the latest Octave version ==end of your script.
Please be more specific. What is the latest version, according to you? If you mean the latest released version, be aware that you may still have an older version due to whatever distribution method you're using. There may be a newer version available that you're not aware of due to the distribution method you're using to ==How do I get Octave, and sound input or output in most cases, there is a way to get a newer version via your distribution method (see other wiki pages for [[Octave_for_GNU/Linux|GNU/Linux]], [[Octave_for_MacOS_X|Mac OSX]], and [[Octave_for_Windows|Windows]]).?==
Sound input from a sound card and output to a sound card is fully supported since Octave 4.0.0 for all platforms. If you mean have problems with the latest Mercurial revision[http://www.octave.org/doc/interpreter/Audio-Processing.html audio I/O functions] using Octave 4.0.0 or a newer version, please specify which one that is. "Latest tip" is not informative, because from the time you wrote "latest tip" to report them on the time someone reads that message, "latest tip" might have changed meaning[http://bugs. Also, you might be standing on a different commit than what "hg tip" saysoctave. The tip may be on a different branch, or you might have updated to a different revision different from what "hg tip" saysorg bug tracker].
Instead, report ==I have problem X using the output of "hg summary" or "hg id". Also please use hashes instead or in addition to revision numbers. Revision numbers are just a convenience and only make sense in your local repo, and might not coincide with what someone sees on their own repo. Hashes are globally unique across all repos.latest Octave version==
If your problem truly persists with the latest version, as indicated [http://www.gnu.org/software/octave/download.html here], then by all means report a bug or ask for help, but don't Please be surprised if volunteers are less inclined to help more specific about what you with a problem that only exists in an older mean by "latest version of Octave."?
== Why * The latest stable version is this floating point computation wrong? =={{Release}}. Be aware that you may still have an older version due to whatever distribution method you are using. To get a newer stable version for your system see for example [[Octave for GNU/Linux|GNU/Linux]], [[Octave for macOS|macOS]], or [[Octave for Microsoft Windows|Windows]]).
Floating point arithmetic is an approximation '''in binary''' to arithmetic on real or complex numbers. Just like * If you cannot represent 1/3 exactly in decimal arithmetic (0.333333 is only a rough approximation refer to 1/3)the latest Mercurial revision, you cannot represent some fractions like $1please specify the [https:/10</math> exactly in base 2www.mercurial-scm. In binaryorg/wiki/ChangeSetID changeset ID] not the revision number, e.g. the representation to one tenth is output of <mathcode>0.0\overline{0011}_bhg summary</mathcode> where the bar indicates that it repeats infinitely (like how or <mathcode>1/6 = 0.1\overline{6}_dhg id</mathcode> in decimal). Because this infinite repetition cannot be represented exactly with a finite number of digits, rounding errors occur for values that appear to be exact in decimal but Changeset IDs are in fact approximations in binary, such as for example how 0.3 - 0.2 - 0.1 is not equal to zeroglobally unique across all repos. In additionIf your problem truly persists with the "latest version", some advanced operations are computed by approximation and are not guaranteed to be accurate, see then please [http://bugs.octave.org/ report a bug] or ask for help at[https://enlists.wikipediagnu.org/wikimailman/listinfo/Rounding#Tablehelp-makeroctave help@octave.27s_dilemma Table-maker's dilemmaorg]. Their results Otherwise, don't be surprised if volunteers are system-dependentless inclined to help you with a problem that only exists in an older version of Octave and is already fixed in a newer version. This isn't an Octave bug. It happens with any program that uses [http://en.wikipedia.org/wiki/IEEE_754 IEEE 754 floating point arithmetic]. To be fair, IEEE 754 also specifies decimal floating point arithmetic, which has never seen wide adoption. The reason why Octave and other programs use IEEE 754 binary floats ==Why is that they are ''fast'', because they are implemented in hardware or system libraries. Unless you are using very exotic hardware, Octave will use your computer's processor for basic floating -point arithmetic.computation wrong?== Like death and taxes, rounding errors are a fact of lifeFloating-point arithmetic is an approximation '''in binary''' to arithmetic on real or complex numbers. You Just like you cannot avoid themrepresent 1/3 exactly in decimal arithmetic (0.333333.. You can . is only move a rounding error from one part of a computation rough approximation to another1/3), or you can use more precision and delay the rounding errorcannot represent some fractions like [itex]1/10$ exactly in base 2. One way to delay In binary, the rounding error is representation to use arbitrary precision arithmetic, which one tenth is inevitably slower as $0.0\overline{0011}_b$ where the bar indicates that it has repeats infinitely (like how $1/6 = 0.1\overline{6}_d$ in decimal). Because this infinite repetition cannot be represented exactly with a finite number of digits, rounding errors occur for values that appear to be implemented exact in software instead of hardwaredecimal but are in fact approximations in binary, such as for example how 0.3 - 0.2 - 0. You may use the vpa function from the symbolic package for this purpose1 is not equal to zero.
Another approach In addition, some advanced operations are computed by approximation and are not guaranteed to the problem is interval arithmetic with the be accurate, see [[Interval packagehttps://en.wikipedia.org/wiki/Rounding#Table-maker.27s_dilemma Table-maker's dilemma]]. Then, the exact result would always be enclosed by two binary floats. Again, this is slower since only the most basic interval arithmetic operations can be performed in hardware Their results are system-dependent.
To learn more about floating point arithmetic, consult This isn't an Octave bug. It happens with any program that uses [httphttps://en.wikipedia.org/wiki/Floating_point_arithmetic its Wikipedia articleIEEE_754 IEEE 754 floating-point arithmetic] or the classical reference [http://. To be fair, IEEE 754 also specifies decimal floating-pointarithmetic, which has never seen wide adoption. The reason why Octave and other programs using IEEE 754 binary floating-guipoint numbers is that they are ''fast'', because they are implemented in hardware or system libraries.de/ What Every Computer Scientist Should Know About Floating Point Arithmetic] Unless you are using very exotic hardware, Octave will use your computer's processor for basic floating-point arithmetic.
== I have installed a Another approach to deal with rounding errors is interval arithmetic with the [[Interval package but still get a "foo undefined" error ==]] or symbolic computatons with the [[Symbolic package]]. These approaches are likely to be slower, since not all operations can be performed on Hardware like pure floatin-point arithmetic.
== Missing lines when printing under Windows with OpenGL toolkit and Intel integrated GPU ==
Some windows users with integrated Intel GPUs have reported missing lines when printing with an OpenGL toolkit like FLTK or Qt. {{bug|42534}}
Users with this kind of problem should try to install/update their Intel OpenGL drivers for Windows or consider installing Mesa drivers from http://qt-project.org/wiki/Cross-compiling-Mesa-for-Windows.
== Plot hangs and makes the GUI unresponsive ==
If the Qt graphics toolkit is used and "plot" is used for the first time, the fontconfig scanner searches the font directory to build a font cache. This can take up to 3min on slow CPUs. See {{bug|45458}}
==Error message about invalid call to script or invalid use of script in index expression== If Octave shows an error message about {{Codeline|invalid call to script .../close.m}} or {{Codeline|invalid use of of script .../close.m in index expression}}, it means that you have created a script called close.m that is overriding the built-in Octave function {{Codeline|close}}. Octave functions and scripts share the samem global namespace. It is best to avoid creating your own scripts or functions that have the same name as an Octave function. = Differences between Octave and Matlab =
<blockquote>
I wrote some code for Matlab, and I want to get it running under Octave. Is there anything I should watch out for?
</blockquote>
<blockquote>
I wrote some code in Octave, and want to share it with Matlab users. Is there anything I should watch out for?
</blockquote>
which is not quite the same thing. There are still a number of differences between Octave and Matlab, however in general differences between the two are considered as bugs. Octave might consider that the bug is in Matlab and do nothing about it, but generally functionality is almost identical. If you find an important functional difference between Octave behavior and Matlab, then you should send a description of this difference (with code illustrating the difference, if possible) to http://bugs.octave.org.
Furthermore, Octave adds a few syntactical extensions to Matlab that might cause some issues when exchanging files between Matlab and Octave users.
You should also look at the pages http://octave.sourceforge.net/packages.php and http://octave.sourceforge.net/docs.html that have a function reference that is up to date. You can use this function reference to see the number of octave functions that are available and their Matlab compatibility.
== Nested Functions ==Octave has limited support for nested functions. That is
Octave has limited support for nested functions since version 3.8.0. That is <syntaxhighlight lang="Matlab">function y = foo (x) y = bar(x) function y = bar (x) y = ...; end end</syntaxhighlight>
is equivalent to
<syntaxhighlight lang="Octave">function y = foo (x) y = bar(x) end function y = bar (x) y = ...; endendfunction
function y = bar (x) y = ...;endfunction</syntaxhighlight> The main difference with Matlab is a matter of scope. While nested functions have access to the parent function's scope in Matlab, no such thing is available in Octave, due to how Octave essentially “un-nests” nested functions.
The authors of Octave consider the nested function scoping rules of Matlab to be more problems than they are worth as they introduce difficult to find bugs as inadvertently modifying a variable in a nested function that is also used in the parent is particularly easy for those not attentive to detail.
== Differences in core syntax ==
There are a few core Matlab syntaxes that are not accepted by Octave, these being
* Some limitations on the use of function handles. The major difference is related to nested function scoping rules (as above) and their use with function handles.
* Some limitations of variable argument lists on the LHS of an expression, though the most common types are accepted.
* Matlab classdef object oriented programming is not yet only partially supported, though work is underway in a branch of the development treesee [[classdef]] for details.
== Differences in core functions ==
A large number of the Matlab core functions (ie i.e. those that are in the core and not a toolbox) are implemented, and certainly all of the commonly used ones. There are a few functions that aren't implemented, usually to do with specific missing Octave functionality (GUI, DLL, Java, ActiveX, DDE, web, and serial functions). Some of the core functions have limitations that aren't in the Matlab version. For example the {{manual|sprandn }} function can not force a particular condition number for the matrix like Matlab can. Another example is that testing and the runtests function work differently in Matlab and Octave.
== Just-In-Time compiler ==
Matlab includes a "Just-In-Time" compiler. This compiler allows the acceleration of for-loops in Matlab to almost native performance with certain restrictions. The JIT must know the return type of all functions called in the loops and so you can't include user functions in the loop of JIT optimized loops. Octave doesn't have has a [[JIT|not fully functional JIT and so to some might seem slower than Matlabcompiler]]. For this reason you must [[Performance#Vectorization|vectorize your code ]] as much as possible. The MathWorks themselves have a good document discussing vectorization at http://www.mathworks.com/support/tech-notes/1100/1109.html.
== Compiler ==
On a related point, there is no Octave compiler, and so you can't convert your Octave code into a binary for additional speed or distribution. There have been several aborted attempts at creating an Octave compiler. Should the JIT compiler above ever be implemented, an Octave compiler should be more feasible.
== Graphic handles ==
Up to Octave 2.9.9 there was no support for graphic handles in Octave itself. In the 3.2.N versions of Octave and beyond, the The support for graphics handles is converging towards full compatibility. The patch function is currently limited to 2-D patches If you notice any incompatibilities, due to an underlying limitation in gnuplot, but the experimental OpenGL backend is starting to see an implementation of 3-D patchesplease [http://bugs.octave.org report a bug].
== GUI functions ==
There are no The support for [http://www.octave.org/doc/interpreter/GUI-Development.html Matlab compatible GUI functions yet] was added in Octave version 3.6.0 and is converging towards full compatibility. This might be an issue if If you intend to exchange Octave code with Matlab users. There are a number of bindings from Octave to {{Forge|tcl-octave|Tcl/Tk}}notice any incompatibilities, please [http://octavizbugs.sourceforgeoctave.net/index.php? VTKorg report a bug] and {{Forge|zenity}} for example, that can be used for a GUI, but these are not Matlab compatible. Work on a Matlab compatible GUI is in an alpha stage in the QtHandles project, which may form part of a future release of Octave.
Octave itself includes no Simulink support. Typically the simulink models lag research and are less flexible, so shouldn't really be used in a research environment. However, some Matlab users that try to use Octave complain about this lack.
== MEX-Files ==
Octave includes an [http://www.octave.org/doc/interpreter/Mex_002dFiles.html API to the Matlab MEX interface]. However, as MEX is an API to the internals of Matlab and the internals of Octave differ from Matlab, there is necessarily a manipulation of the data to convert from a MEX interface to the Octave equivalent. This is notable for all complex matrices, where Matlab stores complex arrays as real and imaginary parts, whereas Octave respects the C99/C++ standards of co-locating the real/imag parts in memory. Also due to the way Matlab allows access to the arrays passed through a pointer, the MEX interface might require copies of arrays (even non complex ones).
Block comments denoted by {{Codeline|<code>#{}} </code> and {{Codeline|<code>#&#125;}} </code> markers (or {{Codeline| <code>%{}} </code> and {{Codeline|<code>%&#125;}}</code>) are supported by Octave with some limitations. The major limitation is that block comments are not supported within [] or {}.
== Mat-File format ==
There are some differences in the mat v5 file format accepted by Octave. Matlab recently introduced the "-V7.3" save option which is an HDF5 format which is particularly useful for 64-bit platforms where the standard Matlab format can not correctly save variables. Octave accepts HDF5 files, but is not yet compatible with the "-v7.3" versions produced by Matlab.
Although Octave can load inline function handles saved by Matlab, it can not yet save them.
Finally, some multi-byte Unicode characters aren't yet treated in mat-files.
== Profiler ==
Thanks to Daniel Kraft's 2011 Google Summer of Code project, [http://www.octave.org/doc/interpreter/Profiling.html Octave has a profiler ] since version 3.6.0. However, at the moment it only produces text output and has its own makeshift interface for hierarchical profiling.
== Toolboxes ==
Octave is a community project and so the toolboxes that exist are donated by those interested in them through [[Octave Forge]]. These might be lacking in certain functionality relative to the Matlab toolboxes, and might not exactly duplicate the Matlab functionality or interface.
== Short-circuit {{Codeline|<code>&}} </code> and {{Codeline<code>|&#124;}} </code> operators ==
The {{Codeline|<code>&}} </code> and {{Codeline<code>|&#124;}} </code> operators in Matlab short-circuit when included in a condition (e.g. an {{Codeline|if}} or {{Codeline|while}} statement) and not otherwise. In Octave only the {{Codeline|<code>&&}} </code> and {{Codeline<code>||&#124;&#124;}} </code> short circuit. Note that this means that
<syntaxhighlight lang="Octave">if (a | b) ... end</syntaxhighlight>
and
<syntaxhighlight lang="Octave">t = a | b; if (t) ... end</syntaxhighlight> have different semantics in Matlab. This is really a Matlab bug, but there is too much code out there that relies on this behavior to change it. Prefer the <code>&&</code> and <code>||</code> operators in {{Codeline|if}} statements if possible.
have different semantics in Note that the difference with Matlab. This is really also significant when either argument is a Matlab bug, but there function with side effects or if the first argument is too much code out there that relies on this behaviour to change it. Prefer a scalar and the {{Codeline|&#124;&#124;}} and {{Codeline|&&}} operators in {{Codeline|if}} statements if possiblesecond argument is an empty matrix. If you need to use code written for Matlab that depends on this buggy behaviour For example, you can enable it since Octave 3.4.0 with note the following command:difference between
do_braindead_shortcircuit_evaluation<syntaxhighlight lang="Octave">t = 1 | []; ## results in [], so...if (t) 1, end ## in if ([]), this is false.</syntaxhighlight>
Note that the difference with Matlab is also significant when either argument is a function with side effects or if the first argument is a scalar and the second argument is an empty matrix. For example, note the difference between
t <syntaxhighlight lang= "Octave">if (1 | []; ## results in [], so... if (t) 1, end ## in if ([]), this short circuits so condition is falsetrue.</syntaxhighlight>
andIn the latter case, Octave displays since version 4.0.0 a warning:
if (1 | []) 1, end ## warning: Matlab-style short circuits so condition is true.-circuit operation performed for operator |
Another case that is documented in the Matlab manuals is that
<syntaxhighlight lang="Matlab">t = [1, 1] | [1, 2, 3]; ## error if ([1, 1] | [1, 2, 3]) 1, end ## OK</syntaxhighlight>
Also Matlab requires the operands of {{Codeline|<code>&&}} </code> and {{Codeline<code>||&#124;&#124;}} </code> to be scalar values but Octave does not (it just applies the rule that for an operand to be considered true, every element of the object must be nonzero or logically true).
Finally, note the inconsistence of thinking of the condition of an {{Codeline|if}} statement as being equivalent to {{Codeline|all(X(:))}} when {{Codeline|X}} is a matrix. This is true for all cases EXCEPT empty matrices:
<syntaxhighlight lang="Matlab">if ([0, 1]) == if (all ([0, 1])) ==> i.e., condition is false. if ([1, 1]) == if (all ([1, 1])) ==> i.e., condition is true.</syntaxhighlight>
However,
<syntaxhighlight lang="Matlab">if ([])</syntaxhighlight>
is not the same as
<syntaxhighlight lang="Matlab">if (all ([]))</syntaxhighlight>
because, despite the name, the {{Codelinemanual|all}} is really returning true if none of the elements of the matrix are zero, and since there are no elements, well, none of them are zero. This is an example of [httphttps://en.wikipedia.org/wiki/Vacuous_truth vacuous truth]. But, somewhere along the line, someone decided that {{Codeline|if ([])}} should be false. The Mathworks probably thought it just looks wrong to have {{Codeline|[]}} be true in this context even if you can use logical gymnastics to convince yourself that "all" the elements of an empty matrix are nonzero. Octave however duplicates this behavior for {{Codeline|if}} statements containing empty matrices.
== Solvers for singular, under- and over-determined matrices ==
Matlab's solvers as used by the operators {{manual|mldivide (}} <code>\) </code> and {{manual|mrdivide (}} <code>/</)code>, use a different approach than Octave's in the case of singular, under-, or over-determined matrices. In the case of a singular matrix, Matlab returns the result given by the LU decomposition, even though the underlying solver has flagged the result as erroneous. Octave has made the choice of falling back to a minimum norm solution of matrices that have been flagged as singular which arguably is a better result for these cases.
In the case of under- or over-determined matrices, Octave continues to use a minimum norm solution, whereas Matlab uses an approach that is equivalent to
<syntaxhighlight lang="Octave">function x = mldivide (A, b) m = rows(A); [Q, R, E] = qr(A); x = [A \ b, E(:, 1:m) * (R(:, 1:m) \ (Q' * b))] end</syntaxhighlight>
While this approach is certainly faster and uses less memory than Octave's minimum norm approach, this approach seems to be inferior in other ways.
A numerical question arises: how big can the null space component become, relative to the minimum-norm solution? Can it be nicely bounded, or can it be arbitrarily big? Consider this example:
<syntaxhighlight lang="Octave">m = 10; n = 10000; A = ones(m, n) + 1e-6 * randn(m,n); b = ones(m, 1) + 1e-6 * randn(m,1); norm(A \ b)</syntaxhighlight>
while Octave's minimum-norm values are around about 3e-2, Matlab's results are 50-times larger. For another issue, try this code:
<syntaxhighlight lang="Octave">m = 5; n = 100; j = floor(m * rand(1, n)) + 1; b = ones(m, 1); A = zeros(m, n); A(sub2ind(size(A),j,1:n)) = 1; x = A \ b; [dummy~,p] = sort(rand(1,n)); y = A(:,p)\b; norm(x(p)-y)</syntaxhighlight>
It shows that unlike in Octave, {{manual|mldivide }} in Matlab is not invariant with respect to column permutations. If there are multiple columns of the same norm, permuting columns of the matrix gets you different result than permuting the solution vector. This will surprise many users.
Since the {{manual|mldivide (}} <code>\) </code> and {{manual|mrdivide (}} <code>/</) code> operators are often part of a more complex expression, where there is no room to react to warnings or flags, it should prefer intelligence (robustness) to speed, and so the Octave developers are firmly of the opinion that Octave's approach for singular, under- and over-determined matrices is a better choice than Matlab's.
== Octave extensions ==
The extensions in Octave over MATLAB syntax are very useful, but might cause issues when sharing with Matlab users. A list of the major extensions that should be avoided to be compatible with Matlab are:
Octave has a lisp-like {{Codeline|unwind_protect}} block that allows blocks of code that terminate in an error to ensure that the variables that are touched are restored. You can do something similar with try/catch combined with {{Codeline|rethrow (lasterror ())}} in Matlab, however rethrow and lasterror are only available in Octave 2.9.10 and later. MATLAB 2008a also introduced {{Codeline|OnCleanUp}} that is similar to {{Codeline|unwind_protect}}, except that the object created by this function has to be explicitly cleared in order for the cleanup code to run.
Note that using try/catch combined with {{Codeline|rethrow (lasterror ())}} can not cannot guarantee that global variables will be correctly reset, as it won't catch user interrupts with Ctrl-C. For example
<syntaxhighlight lang="Matlab">global a a = 1; try _a = a; a = 2 while true end catch fprintf ('caught interrupt\n'); a = _a; rethrow (lasterror()); end</syntaxhighlight>
compared to
<syntaxhighlight lang="Octave">global a a = 1; unwind_protect _a = a; a = 2 while true end unwind_protect_cleanup fprintf ('caught interrupt\n'); a = _a; end</syntaxhighlight>
Typing Ctrl-C in the first case returns the user directly to the prompt, and the variable ''<code>a'' </code> is not reset to the saved value. In the second case the variable ''<code>a'' </code> is reset correctly. Therefore Matlab gives no safe way of temporarily changing global variables.
Indexing can be applied to all objects in Octave and not just variables. Therefore {{Codeline|sin(x)(1:10)}} for example is perfectly valid in Octave but not Matlab. To do the same in Matlab you must do {{Codeline|y &#61; sin(x); y &#61; y([1:10]);}}
Character strings in Octave can be denoted with double or single quotes. There is a subtle difference between the two in that escaped characters like {{Codeline|\n}} (newline), {{Codeline|\t}} (tab), etc are interpreted in double quoted strings but not single quoted strings. This difference is important on Windows platforms where the {{Codeline|\}} character is used in path names, and so single quoted strings should be used in paths. MATLAB doesn't have double quoted strings and so they should be avoided if the code will be transferred to a MATLAB user.

==What features are unique to Octave?==

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

=== 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:

<syntaxhighlight lang="Octave">
>> function s = hello_string (to_who)
> ## Say hello
> if nargin<1, to_who = "World"; end
> s = ["Hello ",\
> to_who];
> endfunction
>> hello_string ("Moon")
ans = Hello Moon
</syntaxhighlight>

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 (...)}})

Note: MATLAB R2016b added the ability to [http://www.mathworks.com/help/matlab/matlab_prog/local-functions-in-scripts.html define functions in script files].

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.

===Strings delimited by double quotes "===

In 2016, Matlab introduced String Arrays, that are initialized by using double quoted strings, and are not implemented in Octave yet. In Octave double-quoted strings include backslash interpretation (like C++, C, and Perl) while single quoted are uninterpreted (like Matlab and Perl).

===Line continuation by backslash===

Lines can be continued with a backslash, {{Codeline|\}}, in addition to three points {{Codeline|...}} as in Matlab.

===Informative block closing===

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.

===Coherent syntax===

Indexing other things than variables is possible, as in:

<syntaxhighlight lang="Octave">
>> [3 1 4 1 5 9](3)
ans = 4
>> cos([0 pi pi/4 7])(3)
ans = 0.70711
</syntaxhighlight>

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.

===Exclamation mark as not operator===

The exclamation mark {{Codeline|!}} (aka “Bang!”) is a negation operator, just like the tilde {{Codeline|~}}:

<syntaxhighlight lang="Octave">
>> if ! strcmp (program_name, "octave"),
> "It's an error"
> else
> "It works!"
> end
ans = It works!
</syntaxhighlight>

Note however that Matlab uses the {{Codeline|!}} operator for shell escapes, for which Octave requires using the system command.

===Increment and decrement operators===

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|+&#61;}}, {{Codeline|-&#61;}}, {{Codeline|*&#61;}}, {{Codeline|/&#61;}}, {{Codeline|^&#61;}},{{Codeline|.+&#61;}},{{Codeline|.-&#61;}},{{Codeline|.*&#61;}}, {{Codeline|./&#61;}} and {{Codeline|.^&#61;}}.

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}}.

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.

For matrix and vector arguments, the increment and decrement operators work on each element of the operand.

===Unwind-protect===

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:

<syntaxhighlight lang="Octave">
unwind_protect
body
unwind_protect_cleanup
cleanup
end_unwind_protect
</syntaxhighlight>

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.

The unwind_protect statement is often used to reliably restore the values of global variables that need to be temporarily changed.

Matlab can be made to do something similar with their {{manaul|onCleanup}} function that was introduced in 2008a. Octave also has {{manual|onCleanup}} since version 3.4.0.

===Built-in ODE and DAE solvers===

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.

===Do-Until loop structure===

Similar to the do-while loop in C and C++, Octave allows a do-until loop which does not exist in Matlab:

<syntaxhighlight lang="Octave">
x = 0
do
x += 1;
until (x == 10)
</syntaxhighlight>

<syntaxhighlight lang="Octave">
f = (1:0.1:2);
# put angular frequencies on the first dimension to prepare broadcasting
omega = 2 * pi * f(:);
# time is already on the second dimension (row vector)
t = 0:0.02:2;
# the resulting s will be a 2-dimensional array
s = sin(omega .* t);
# which can be displayed as
pcolor(t, f, s)
xlabel("t (s)")
ylabel("f (Hz)")
</syntaxhighlight>

Note: [https://www.mathworks.com/help/matlab/matlab_prog/compatible-array-sizes-for-basic-operations.html Automatic expansion of dimensions] was added to MATLAB R2016b.

===Documentation strings===

Octave allows extensive formatting of the help string of functions using Texinfo. The effect on the online documentation is relatively small, but makes the help string of functions conform to the help of Octave’s own functions. However, the effect on the appearance of printed or online documentation will be greatly improved.

===Test functions===

Octave allows to add self-tests to user defined functions. Tests are put after function definition in specially commented block.

<syntaxhighlight lang="Octave">
function mult = a(val)
mult = val.*2;
endfunction
%!test
%! assert (a(3), 6);
</syntaxhighlight>

Such a function can be tested for valid outputs by following code:

>> test a
PASSES 1 out of 1 test

===Demonstration Functions===

Example code block can be part of function file in a similar manner as test functions. For example to run {{manual|demo}} for function multinom of package specfun, use:

demo multinom

===Powerful assert===

Function assert have extended input possibilities.
=[https://en.wikipedia.org/wiki/Graphical_user_interface GUI]=
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.

=Development=

==When will feature X be released or implemented?==

When it's ready, sooner [http://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 [http://www.octave.org/commercial-support.html developers may be convinced to work on your specific problem for some money].

==How can I get involved in Octave development?==

Be around. Be social. Participate in our mailing lists [https://lists.gnu.org/mailman/listinfo/help-octave help@octave.org] and [https://lists.gnu.org/mailman/listinfo/octave-maintainers maintainers@octave.org]. Find things about Octave you don't like, and start thinking about how to fix them. Many people who now contribute to Octave first spent several years helping in the mailing list before they started to delve into the code. A good way to learn Octave is to understand the problems other people are having with it, so being helpful in the mailing lists not only helps Octave as a whole, but it also prepares you to be a better Octave contributor.

If you feel ready to dive right into the code, read the [[Developers]] wiki page or [http://www.octave.org/get-involved.html start here]. But do not send an email to the mailing lists listing your skills and offering to help. We won't just suggest things for you to do. We lack volunteers and we do need your help, but because of that, we also lack the time to provide good guidance and mentoring. If there is a specific short-term project you would like to work on, say so, and just do it. Then ask for help or advice when you're doing it. It is a lot more important that you do something that you're actually interested on than something we suggested because it only matches your skills.

We also need help with this wiki and the [http://www.octave.org/doc/interpreter/ manual]. These are also important tasks. The documentation is easy to patch, and the help text for individual functions even more so. Editing this wiki is even easier.

Accurate bug reporting is also very useful. Find and report [http://bugs.octave.org/ bugs], making an attempt to diagnose them. Eventually, you will also know how to fix them. If you want to help with bug reports or patches, subscribe to the [https://lists.gnu.org/mailman/listinfo/octave-bug-tracker 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.

Look at our [[projects]], [[short projects]], and [[Summer of Code Project Ideas]] if you need specific inspiration for coding tasks that we would like to get done.
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