Optional args in MATLAB functions

Question

How can I declare function in MATLAB with optional arguments   For example  function  a    train x  y  opt   where opt must be an optional argument

User · Accepted Answer

There are a few different options on how to do this. The most basic is to use varargin, and then use nargin, size etc. to determine whether the optional arguments have been passed to the function.

% Function that takes two arguments, X & Y, followed by a variable 
% number of additional arguments
function varlist(X,Y,varargin)
   fprintf('Total number of inputs = %d\n',nargin);

   nVarargs = length(varargin);
   fprintf('Inputs in varargin(%d):\n',nVarargs)
   for k = 1:nVarargs
      fprintf('   %d\n', varargin{k})
   end

A little more elegant looking solution is to use the inputParser class to define all the arguments expected by your function, both required and optional. inputParser also lets you perform type checking on all arguments.

User · Answer

A simple way of doing this is via nargin  N arguments in   The downside is you have to make sure that your argument list and the nargin checks match    It is worth remembering that all inputs are optional  but the functions will exit with an error if it calls a variable which is not set  The following example sets defaults for b and c  Will exit if a is not present   function   output args     input example  a  b  c   if nargin  lt  1   error  input example    a is a required input   end  if nargin  lt  2   b   20 end  if nargin  lt  3   c   30 end end

User · Answer

A good way of going about this is not to use nargin  but to check whether the variables have been set using exist  opt    var     Example   function  a    train x  y  opt      if   exist  opt    var            opt   true      end end   See this answer for pros of doing it this way  How to check whether an argument is supplied in function call

[function] Optional args in MATLAB functions

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