matlab programming differences between octave and matlab

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MATLAB Programming/Differences betweenOctave and MATLAB

Octave has been mainly built with MATLAB compati-

bility in mind. It has a lot of features in common with

MATLAB:

1. Matrices as fundamental data type.

2. Built-in support for complex numbers.

3. Powerful built-in math functions and extensive func-

tion libraries.

4. Extensibility in the form of user-defined functions.

Some of the differences that do exist between Octave and

MATLAB can be worked around using user preference

variables.

GNU Octave is mostly compatible with MATLAB. How-

ever, Octaves parser allows some (often very useful) syn-

tax that MATLABs does not, so programs written for

Octave might not run in MATLAB. For example, Octave

supports the use of both single and double quotes. MAT-

LAB only supports single quotes, which means parsingerrors will occur if you try to use double quotes (e.g. in an

Octave script when run on MATLAB). Octave and MAT-

LAB users who must collaborate with each other need to

take note of these issues and program accordingly.

Note:Octave can be run in traditional mode

(by including the --traditional flag when start-

ing Octave) which makes it give an error when

certain Octave-only syntax is used.

This chapter documents instances where MATLABs

parser will fail to run code that will run in Octave, andinstances where Octaves parser will fail to run code that

will run in MATLAB. This page also contains notes on

differences between things that are different between Oc-

tave (in traditional mode) and MATLAB.

1 C-Style Autoincrement and As-

signment operators

Octave supports C-style autoincrement and assignment

operators:

i++; ++i; i+=1; etc.

MatLab does not.

2 Temporaries

Octave and MATLAB support temporary expressions.

tmp = size(mtx); columns = tmp(2); % works in both

columns = size(mtx)(2); % works in Octave, fails in

MATLAB columns = size(mtx,2); % works in both

3 Product of booleans

MATLAB (R2011b) and Octave (3.6.4) responds differ-

ently when computing the product of boolean values:

X = ones(2,2) ; prod(size(X)==1) MATLAB: PROD is

only supported for floating point input. Octave: ans = 0

4 nargin

Nargin returns the number of input arguments of a func-tion. MATLAB (R2011b) will not allow the following;

Octave will.

function myfun = testfun(c) if (nargin == 1) nargin = 2;

else nargin = 3 end

5 startup.m

MATLAB will execute a file named 'startup.m' in the di-

rectory it was called from on the command line. Octave

does not. It will, however, execute a file named '.octaverc'which can be edited to execute existing files. This means

that '.octaverc' can be edited to look for and execute a

'startup.m' file.

if ( exist ('startup.m', 'file') ) source ('startup.m') # load

startup.m like MATLAB endif

6 ['abc ';'abc']

['abc ';'abc'] is allowed in Octave; MATLAB returns: ??Error using ==> vertcat

In Octave the result will be a 2 by 4 matrix.

1


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2 14 SOME OTHER DIFFERENCES

7 Calling Shells

the "! STRING syntax calls a shell with command

STRING in MATLAB. Octave does not recognize ! as

system call, since it is used in logical operations. Always

use 'system (STRING)' for compatibility.

If you really miss the one-character shortcut, for con-

venience on the command line you can create a similar

shortcut by defining the following in your '.octaverc' file:

function S(a), system(a); end

Now S STRING will evaluate the string in the shell.

8 Attempting to load empty files

MATLAB lets you load empty files, OCTAVE does not.

system('touch emptyfile'); A = load('emptyfile') MAT-LAB R2011b : A=[] Octave 3.6.2 : error: load: file `emp-

tyfile' seems to be empty! error: load: unable to extract

matrix size from file `emptyfile'

9 fprintf and printf

Octave supports both printf and fprintf as a command for

printing to the screen. MATLAB requires fprintf:

foo = 5; printf ('My result is: %d\n', foo) % Prints to

STDOUT. Octave onlyfprintf covers writing both to the screen and to a file by

omitting the optional file-handle argument:

foo = 5; fprintf('My result is: %d\n', foo) % Prints to

STDOUT. Octave and MATLAB

10 Whitespace

MATLAB does not allow whitespace before the trans-

pose operator but Octave does (it is just an operator like

others).

[0 1]' % works in MATLAB and Octave [0 1] ' % works

only in Octave

11 Line continuation

MATLAB always requires ... for line continuation.

rand (1, ... 2)

while Octavealsosupports

rand (1, 2)

and

rand (1, \ 2)

12 Logical operator NOT

Octave allows users to use both ~ and ! with boolean

values. The first is for MATLAB compatibility, while

! will be more familiar to C/Java/etc programmers. If

you use the latter, however, you'll be writing code that

MATLAB will not accept:

For not-equal comparison, Octave can use both '~='

or '!='. MATLAB requires '~='.

13 GNU Octave Control Package

Both MATLAB and Octave have toolboxes intended to

control system design. In Octave, the toolbox is called

the Octave Control Package. The package can be down-

loaded, compiled and installed with the command pkg in-stall control from the Octave prompt. Users of Debian

and its derivatives can install it by installing the package

octave-control, if it is not installed by default.

For more information about functions syntax, type help

. For more information about the

Control Package, view the PDF manual in the packages

doc folder.

Small differences exist - an example is c2d. Here are the

two formats for the bilinear transformation with an analog

model C:

discrete = c2d(C,0.5,'tustin'); % Matlab

discrete = c2d(C,0.5,'bi'); % GNU Octave

14 Some other differences

MATLAB uses the percent sign '%' to begin a com-

ment. Octave uses both the hash symbol # and the

percent sign % interchangeably.

For exponentiation, Octave can use ^ or **; MAT-

LAB requires ^.

For string delimiters, Octave can use ' or "; MAT-

LAB requires '.

To end blocks, Octave can use end or specify the

block with endif, endfor, ...; MATLAB requires

end.

Octave supports C-style hexadecimal notation (e.g.

0xF0); MATLAB requires the hex2dec function

(e.g. hex2dec('F0')").

If something (like Netlab) need a function called fc-nchk, you can just put the following into a file called

fcnchk.m and put it somewhere Octave can find it:


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function f=fcnchk(x, n) f = x; end

The main difference is thelack of GUIfor Octave.

There have been many attempts to solve this issue

though they are all eventually abandoned once they

no longer work with new Octave versions. There is

an experimental GUI as part of Octave already re-leased, which is planned to become official with the

next release.

15 Notes about specific functions

For dbstep, in use dbstep"; for dbstep, use db-

next

For eig(A,B)" use qz(A,B)"

fputs function is not available in MATLAB. Use

fprintf instead.

page_output_immediately = 1 should this be default

in --traditional?

strread and textscan in Octave 3.4.0 are not fully

compatible with their implementations in MATLAB

2009b (and probably later versions as well). For in-

stance, the N=1 option (repeat reading format un-

til end of string) is not implemented in Octave 3.4.0

. Using a value of N=a positive integer (read format

N times) does work the same as in MATLAB.

textscan function is not included in Octave versions

prior to 3.4.0. Use fscanf instead.

For the linprog function, MATLAB is more permis-

sive by allowing the a and b inputs to be either

row or column vectors. Octave requires that they be

column vectors.

In Octave, one can specify data labels (or legends)

with the plot function, while in MATLAB, one can

only use the legend function.

Octave: plot(x, y, ';label;') MATLAB/Octave: plot(x, y);

legend('label')

The error(msg) function in MATLAB is a no-op ifthe message is empty. In Octave, it results in an er-

ror.

16 References

http://wiki.octave.org/FAQ#How_is_Octave_

different_from_Matlab.3F

17 See also

Octave Programming Tutorial
https://en.wikibooks.org/wiki/Octave_Programming_Tutorialhttp://wiki.octave.org/FAQ#How_is_Octave_different_from_Matlab.3Fhttp://wiki.octave.org/FAQ#How_is_Octave_different_from_Matlab.3Fhttp://wiki.octave.org/FAQ#GUI


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