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FAQ

1,826 bytes removed, 05:23, 28 July 2017
Lots of reordering.
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>
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:
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 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 What documentation exists 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 codeBesides this wiki, read the GNU Octave distribution includes a [[Developers]http://www.octave.org/doc/interpreter 1000+ page Texinfo manual] wiki page or ([http://www.octave.org/get-involvedoctave.html start herepdf PDF]). But do not send an email Access to the mailing lists listing your skills and offering to helpcomplete text of the manual is available via the <code>doc</code> command at the GNU Octave prompt. We won't just suggest things for If you to do. We lack volunteers and we do need your helphave problems using this manual, but because of or find that, we also lack the time to provide good guidance and mentoring. If there some topic is a specific short-term project you would like to work onnot adequately explained, say soindexed, and just do it. Then ask for help or advice when you're doing cross-referenced, please report 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://wwwbugs.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 ==How can I 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-a 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 with.Octave?==
Look at Please read our [[projects]], [[short projects]], and [[Summer of Code Project Ideas]] if you need specific inspiration for coding tasks that we would like to get donewebsite http://www.octave.org/bugs.html.
=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]].
=Installation= ==How can I install Octave on Windows?== :''See: [[Octave for Microsoft Windows]]'' ==How can I install Octave on macOS?== :''See: [[Octave for macOS]]'' ==How can I install Octave on GNU/Linux?== :''See: [[Octave for GNU/Linux]]'' ==How can I install Octave on Android / what is this Octave app in the Google Play store?== There is an '''unofficial''' Octave app available for Android in the Google Play store. This Octave app is no longer freely available and has become [https://en.wikipedia.org/wiki/Shareware#Nagware "nagware"]. This is a sad turn of events. Please see [[Android]] for more information. ==How can I install Octave on platform X?== 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]. ==What Octave 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 obtain Octave's source code?== The latest version of the Octave source code (and older versions) is available from: * http://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 {{codeline|<code>news}} </code> at the Octave prompt. The following changes are a distilled list of the major changes:
==Coming What's new in a future releasethe 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-forge
* 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 Octave?= 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 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. ==Getting additional help== 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. ==User community== To subscribe to the list, go to http://www.octave.org/archive.html and follow the link to the subscription page for the list. Please do not send requests to be added or removed from the mailing list, or other administrative trivia to the list itself. An archive of old postings to the help-octave mailing list is maintained on http://www.octave.org/archive.html. 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 We also have [http://webchat.freenode.net?channels=octave&uio=d4 an IRC chat room], <code>#octave</code> in Freenode. ==I think I have found a bug in Octave.== “I think I have found a bug in Octave, but I'm not sure. How do I know, and who should I tell?” First, see the section [http://www.octave.org/bugs.html on bugs and bug reports in the 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. =How can I obtain Octave?= ==Source code== Source code is available on the Octave development site, where you are sure to get the latest version. * http://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, or from the Octave website. ==Pre-compiled binaries ==:''See also: [[Build from source]]'' The Octave project does not normally distribute its own binaries, but other projects do. For example, Linux and BSD distributions provide by their respective Octave binaries.Windows is a recent exception, in that binaries are available directly from the Octave project (starting from version 4.0).For an up-to-date listing, see: * http://www.octave.org/download.html
As of today, Octave binaries are available at least on Debian, Ubuntu, RedHat, Suse, and Fedora GNU/Linux; Mac OS X; and Windows (versions 98, 2000, XP, Vista, 7, 8, and 10). ==How do I get a copy of Octave for (some other platform)?== 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].==How can I install Octave on Android? What is this Octave app in the Google Play store?== There is an unofficial Octave app available for Android in the Google Play store. Please see [[Android]] for more information. This version of Octave is no longer freely available and has become 'nagware'. This is a sad turn of events. =Installation issues and problems=  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). Check out the page [[Installation]] for more detailed information about installing Octave. ==What else do I need?== 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. '''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. ==Can I compile Octave with another C++ compiler?== Yes, but development is done primarily with GCC, so you may hit some incompatibilities. Octave is intended to be portable to any standard conforming compiler. If you have difficulties that you think are bugs, please report them to the http://bugs.octave.org bug tracker, or ask for help on the [mailto:help@octave.org mailing list]. == How do install or load all Octave -Forge packages? ==
Do not do it! Really, there is no reason to do this. Octave has many
remember that your programs still need to load the packages they require.
=Coding= ==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:  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 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]. ===Comments with #=== 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 "=== 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). ===Line continuation by backslash=== Lines can be continued with a backslash, {{Codeline|\}}, in addition to three points {{Codeline|...}}. See the previous example. ===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:  octave:1> [3 1 4 1 5 9](3) ans = 4 octave:2> cos([0 pi pi/4 7])(3) ans = 0.70711 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|~}}:  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. ===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:  unwind_protect body unwind_protect_cleanup cleanup end_unwind_protect 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 {{Codeline|onCleanup}} function that was introduced in 2008a. Octave also has {{Codeline|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  x = 0 do x += 1; until (x == 10) ===Broadcasting=== Borrowed from [http://stackoverflow.com/q/26948776/3565696 other languages], [http://www.gnu.org/software/octave/doc/v4.0.1/Broadcasting.html octave broadcasting] allows easy and readable vectorization.  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)") 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. function mult = a(val) mult = val.*2; endfunction %!test %! assert (a(3), 6); Such a function can be tested for valid outputs by following code:  octave:1> 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 demo for function multinom of package specfun, use:  demo multinom ===Powerfull assert===Function assert have extended input possibilities. ==How does Octave solve linear systems?== 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. =How do I...?usage=
==How do I execute an Octave script?==
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]].
 
==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> 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> corr
corr2 corrcoef
==How do I erase a figure?==
==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 HerberFarnsworthHerber Farnsworth? to help-octave on 2003-05-01:
#include <octave/oct.h>
Matrix unis(f_ret(0).matrix_value());
==How do I change colourcolor/line definition in gnuplot postscript?== Here is a awk script to get a rainbow colour color map
#!/bin/awk -f
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 filedirectly)?==
'''This only works with gnuplot as graphics_toolkit, NOT with fltk. See [https://savannah.gnu.org/bugs/?33180 Bug#33180]'''
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.
<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. Instead, initialise initialize the <code>uint64</code> with smaller numbers and perform a computation to get the larger number you want. E.g.,
<syntaxhighlight lang="Octave">uint64(999999999999999) * 10000</syntaxhighlight>
There are no plans to support running P-files produced by Matlab in Octave.
 
==How does Octave solve linear systems?==
 
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.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.
 
==How do I do X?==
 
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> 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> corr
corr2 corrcoef
=Common problems=
By default Octave is set to pass its screen output through a pager (usually the default pager is "less") which allows
things such as navigating through the output with arrow keys or searching for text or regular expressions within the output.
The pager only displays the output after it's finished receiving it, so when it is active you'll not be able to see anything until your script has terminated. To change this behavior temporarily or permanently you may want to use one of the options described [http://www.gnuoctave.org/software/octave/doc/interpreter/Paging-Screen-Output.html here].
==When I try plotting from a script, why am I not seeing anything?==
* Fedora: {{Codeline|octave-devel}}
== I'm having problem XXX X 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 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 Octave's 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 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.
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.
== 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}}
See also https://www.opengl.org/wiki/FAQ#Why_is_my_GL_version_only_1.4_or_lower.3F
== 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}}
= Differences between Octave and Matlab =
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>
<blockquote>
I wrote some code in Octave, and want to share it with Matlab users. Is there anything I should watch out for?
</blockquote>
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
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
* 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. 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 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.
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.
== Short-circuit {{Codeline|&}} and {{Codeline|&#124;}} operators ==
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
end
have different semantics in Matlab. This is really a Matlab bug, but there is too much code out there that relies on this behaviour behavior 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 behaviourbehavior, you can enable it since Octave 3.4.0 with the following command:
do_braindead_shortcircuit_evaluation(1)
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.
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.
== 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:
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:
 
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
 
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].
 
===Comments with #===
 
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 "===
 
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).
 
===Line continuation by backslash===
 
Lines can be continued with a backslash, {{Codeline|\}}, in addition to three points {{Codeline|...}}. See the previous example.
 
===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:
 
octave:1> [3 1 4 1 5 9](3)
ans = 4
octave:2> cos([0 pi pi/4 7])(3)
ans = 0.70711
 
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|~}}:
 
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.
 
===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:
 
unwind_protect
body
unwind_protect_cleanup
cleanup
end_unwind_protect
 
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 {{Codeline|onCleanup}} function that was introduced in 2008a. Octave also has {{Codeline|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
 
x = 0
do
x += 1;
until (x == 10)
 
===Broadcasting===
 
Borrowed from [http://stackoverflow.com/q/26948776/3565696 other languages], [http://www.gnu.org/software/octave/doc/v4.0.1/Broadcasting.html octave broadcasting] allows easy and readable vectorization.
 
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)")
 
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.
function mult = a(val)
mult = val.*2;
endfunction
%!test
%! assert (a(3), 6);
 
Such a function can be tested for valid outputs by following code:
 
octave:1> 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 demo for function multinom of package specfun, use:
 
demo multinom
 
===Powerfull 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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