Octave Compatibility FAQ

Octave is mostly compatible with Matlab. Most matlab functions can be made to run with very little change. With careful coding, you can get your code to run without change in Matlab and Octave. This document outlines the things that you need to watch out for.

You may want to start Octave with the option --traditional, which sets a number flags so that the interpreter handles things in a more compatible way. See the "porting" section of the octave FAQ: http://www.octave.org/FAQ.html#SEC24

Be sure you have a recent development version of octave and install octave-forge.

Resources

octave-forge: http://octave.sf.net
Joao Cardoso's summary of the octave mailing lists: http://merlin.inescn.pt/~qual/Octave/Octave_links.html
Octave mailing list archives: http://www.octave.org/octave-lists/archive/index.html

Language Elements

Q. Do load and save work for structures?
A. Versions of octave after 2.1.53 support loading and saving of structures in all of its file formats.
Q. Does octave support 'end' indexing?
A. Yes, for sufficiently new versions of octave. For older versions, use length(A) or size(A,1) and size(A,2) as you did before matlab added the 'end' indexing syntax.
Q. Why do "grid on" and other commands give me a syntax error?
A. Only Octave built-ins can be ``text functions'' (and only a few are defined to be). Those which are not built-in, you can mark as text functions using the following line in your ~/.octaverc: mark_as_command grid axis Either that or use the functional form: grid('on')
Q. Why isn't Octave seeing my .matlabrc file?
A. Because it is not called .octaverc.
Q. How do I compile my mex functions?
A. See the mex subdirectory of octave-forge/extras.

Q. debugging?
A. it exists but is not well documented

dbstop if error	->	debug_on_error = 1
dbstop in mfile at lineno	->	dbstop (func, line)
dbclear in mfile at lineno	->	dbclear (func, line)
dbquit	->	quit
dbstack	->	dbwhere
dbcont	->	dbg_cont
dbstep in	->	dbg_step
dbstep	->	dbg_next
dbstatus	->	dbstatus

Q. assignin
A. Get a recent version of octave.
Q. [a{:}] = ...
A. Octave can not yet use this construct to define multiple output arguments. Use "[a{1},a{2}] =" instead. It is expected that this will be fixed in a future release.

Types

Q. Does Octave support sparse matrices?
A. Use sparse package in octave-forge.
Q. Does Octave support nD arrays?
A. Yes, for sufficiently recent versions of octave
Q. Does octave support cell arrays?
A. Yes, in recent development versions.
Q. Does octave support different precisions char, short, float, etc?
A. Use 2.1.58 when it is released
Q. Does octave support symbolic variables?
A. Use symbolic package in octave-forge. There is no support for symbolic matrices. Symbolic equivalents to builtin functions use uppercase first letter since Octave can overload built-in functions for user-defined types (see Sparse answer above for alternative).
Q. Does octave support arrays of structures?
A. Yes in recent development versions.

Toolboxes

Q. simulink
A. Doesn't exist. Search for simulink in the octave archives for suggested alternatives.
Q. Is there an optimization tool box?
A. Use octave-forge. This is incomplete. If you need more see Joao's summary of the octave lists.
Q. ODE's?
A. Octave has lsode. octave-forge has matlab style ode23, etc.
Q. Integration?
A. Octave has quad. octave-forge has matlab V5 style quadrature functions. quadl was recently added to octave-forge.
Q. Are there matlab style UI functions?
A. No. some work on Tcl/Tk links to Octave, but it is incomplete. There are two separate branches. See octave archives and octave-forge.
Q. Signal processing package?
A. octave-forge has many functions. Others are available:

vco, modulate, demod
Time Frequency Toolbox
http://www-isis.enst.fr/Applications/tftb/iutsn.univ-nantes.fr/auger/tftb.html
arcov, armcov, prony, pmusic
SPC Tools spline directory
ftp://svr-ftp.eng.cam.ac.uk/pub/comp.speech/tools/spctools/
Q. Statistics toolbox
A. many of the functions exist but often under different names in base octave
Q. Control systems toolbox
A. many of the functions exist but often under different names in base octave

Individual functions

Q. Where do I find the matlab function XXX?
A. Many XXX are in the octave-forge package at http://octave.sf.net. This is a collection of Octave functions contributed by the user community but not (yet) included in Octave. If it is not there, then you can try Joao Cardoso's summary of the octave mailing lists at http://merlin.inescn.pt/~qual/Octave/Octave_links.html or search the Octave mailing list archives directly at http://www.octave.org/octave-lists/archive/index.html You can also search the matlab contributions site and the wider net for alternatives to existing matlab functions.
Q. Why is the title of my graph not showing up on my graph.
A. Octave wants the title before the plot command, matlab wants it after. Try setting automatic_replot = 1
Q. logm doesn't work well for ill-conditioned matrices.
A. logm is a stalled work in progress. Ask pkienzle@users.sf.net to post the work he and Ross Lippert did on this.
Q. eig(A,B)
A. qz(A,B)
Q. Can parameters be passed through the call to fsolve() to the user-supplied function?
A. use FIXES/fsolve.cc on octave-forge.
Q. inmem
A. who -functions
Q. computer
A. exists in octave, but probably returns different output
Q. ! shell command
A. system("shell command")
Q. gallery, compan, hadamard
A. http://www.ma.man.ac.uk/~higham/testmat.html
Q. subspace
A. http://www.mathworks.com/support/ftp/linalgv5.shtml
Q. audio functions
A. octave-forge/main/audio
Q. datetick
A. gset xdata time; gset timefmt "%d/%m"; gset format x "%b %d"