How to support default parameter in MATLAB FUNCTION ?

1 . As I know , there is no default parameter support on MATLAB FUNCTION like other high level programming language c,c++, Is there any other methodology through which it can be done like other compiler C,C++? or programmer has to do using his own logic through varargin.

Answer 1

[Stephen23]

MATLAB is an interpreted language, not a compiled language, so there is no compiler as such.

In any case there is no inbuilt syntax to allow such things as:

function out = fun(val_1=def_val, val_2=def_val2, ...)

But you could use the input parser class, or use one of the methods listed here:

http://blogs.mathworks.com/loren/2009/05/05/nice-way-to-set-function-defaults/

The most common ways of dealing with this are:

• Use nargin and some switch or if statements to detemrine the default parameters.
• Use varargin and logical indexing to detect non-specified arguments (e.g. empty).
• Use key-value pairs (usually with varargin) and strcmpi to detect the keys.
• Use a scalar structure to hold all options.

Using varargin with nargin or logical indexing is very easy:

function foobar(varargin)
Defaults = {A,B,C...};
Defaults(1:nargin) = varargin;

OR

function foobar(varargin)
Defaults = {A,B,C...};
idx = ~cellfun('isempty',varargin);
Defaults(idx) = varargin(idx);

MATLAB themselves use different methods in different functions. Have a look at the ODE functions to see the structure syntax, many plotting functions use the key-value syntax.

You can easily combine key-value and scalar-structure in one function, see my FEX submission here to see how:

http://www.mathworks.com/matlabcentral/fileexchange/47221-numeric-to-english-words

[M.K.H. CHANDAN]

Yes, It is a nice idea, on programer way Defaults(1:nargin) = varargin; we can solve it , also we can store it on an cell array and can be used for further use.

[Jan Siegmund]

This answer is not up to date in my opinion. The arguments Block can deal with default arguments in modern MATLAB.

[Nicholas Ayres]

Jan Siegmund.

Please explain?

[Steven Lord]

New functionality introduced in release R2019b.

[Tong Zhao]

Thanks from 2022

[Ludwig Behringer]

nice

Answer 2

[Jan Siegmund]

The Answers are not up to date. Modern MATLAB supports the arguments Block:

function out = foo(in)
    arguments
        in(1,1) double {mustBeFinite} = 0;
    end
    out = in + 1;
end

For more Info check this Page: https://de.mathworks.com/help/matlab/matlab_prog/function-argument-validation-1.html

Be careful with the validation functions though. They are not "is"-functions returning logical, rather they throw an error. Here is a list of predefined ones: https://de.mathworks.com/help/matlab/matlab_prog/argument-validation-functions.html

If the default argument is a class you may want to use <Class>.empty:

arguments
    nameValueArgs.BaseFigure matlab.ui.Figure = matlab.ui.Figure.empty;
end

[Stephen23]

https://blogs.mathworks.com/pick/2019/09/27/new-with-r2019b-function-argument-validation

Note that the arguments syntax was first introduced in R2019b.

[Jan Siegmund]

Ah thank you Stephen, I thought it would have existed for longer.

Answer 3

[Ingrid]

in your function you need to check how many parameters have been passed

function myFunction(variable1,variable2, optionalVarChangeDefaultParam)
if nargin > 2
  defaultParam = optionalVarChangeDefaultParam;
else
  defaultParam = 2;
end

[M.K.H. CHANDAN]

Yes , It is programmer way , but MATLAB does not support like function myFunction(variable1,variable2,... optionalVarChangeDefaultParam1 =3, ... optionalVarChangeDefaultParam2 =4 , ... optionalVarChangeDefaultParam4 =5)

Answer 4

[Stefan Schuberth]

https://de.mathworks.com/help/matlab/ref/arguments.html?searchHighlight=arguments&s_tid=srchtitle_arguments_1

function testFun(a,b)

arguments a=10; end % default value

arguments b(3,3) double {mustBePositive} = 10; end

% arguments a(size1dim,size2dim) varType {validationFunction} = defaultValue; end

disp(a);

end