MATLAB: How to Define a Default Input Argument for a Function

functioninput argument

How to define a default input argument for a function? I want to set a default input argument which will be replaced later by new values entered by user. How?

Best Answer

function someFunc( someInput )
narginchk( 0, 1 )
if ~exist( 'someInput', 'var' )
   someInput = 7;
end
...
end

Generally I add an extra line something like the following, but I'm fussy:

if exist( 'someInput', 'var' )
   validateattributes( someInput, { 'double' }, { 'scalar', 'nonnegative' } )
else
   someInput = 7;
end

Related Solutions

MATLAB: What’s the function of validateattributes’s argument FUNCNAME and VARNAME

They are used to change the error messages. See for example http://www.mathworks.com/help/matlab/matlab_prog/check-function-inputs-with-validateattributes.html

So if the arguments are being processed by a routine named "checkme", then instead of the message

Error using checkme (line 3)
Expected input to be positive.

you can have it say

Error using FUNCNAME (line 3)
Expected input, VARNAME, to be positive.

MATLAB: Calling a function with 2 inputs using only a single input

It depends how you want to handle it. Do you want 'b' to be an optional argument or do you want to force the caller to always give a value for b and support [] as a a value for it?

As the final argument to a function there is not usually much point doing the latter so I would just do e.g.

function out = myFunction( a, b )
narginchk( 1, 2 )
if exist( 'b', 'var' )
   % Do some validation - optional I suppose!!
else
   b = 0.1;
end

If you wanted to support 'a' being optional then you could do this by allowing [] to be a valid input and would do like above, but include

if exist( 'a', 'var' ) && ~isempty( a )

Best Answer

Related Solutions

MATLAB: What’s the function of validateattributes’s argument FUNCNAME and VARNAME

MATLAB: Calling a function with 2 inputs using only a single input

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