CODEWITHSUNDEEP
matlab
user1681664
user1681664

Reputation: 1811

nargin, vargin, exist, what is the best way to implement optional arguments matlab

I have a function in matlab:

function output = myfunc(a,b,c,d,e)
      %a and b are mandetory
      %c d and e are optional
end

How would I handle inputs if a user gave an optional arg for e but not for c and d?

nargin just gives the number of arguments. would exist be the best way?

Upvotes: 5

Views: 5606

Answers (2)

Andreas H.
Andreas H.

Reputation: 6085

Just use nargin. It will tell you how many arguments are present. Use varargin only when you have a variable number of arguments, that is you have no limit in number of arguments, or you want to access the arguments in an indexing fashion. I assume this is not the case for you, so one solution might look like this.

function output = myfunc(a,b,c,d,e)
  %a and b are mandetory
  %c d and e are optional
  if nargin < 3 || isempty(c)
     c = <default value for c>
  end
  if nargin < 4 || isempty(d)
     d = <default value for d>
  end
  if nargin < 5 || isempty(e)
     e = <default value for e>
  end
  <now do dome calculation using a to e>
  <If a or b is accessed here, but not provded by the caller an error is generated by MATLAB>

If the user does not want to provide a value for c or d but provides e, he has to pass [], e.g. func(a,b,c,[],e), to omit d.

Alternatively you could use 

if nargin == 5
   <use a b c d and e>
elseif nargin == 2
   <use a and b>
else    
   error('two or five arguments required');
end

to check if all a arguments e are present. But this requires exactly 2 or 5 arguments.

Upvotes: 2

Matt
Matt

Reputation: 2802

You can to define c, d and e as optional and then assign values based on position. This requires empty inputs if they want e but not c. For example:

function output = myfunc( a, b, varargin )

optionals = {0,0,0}; % placeholder for c d e with default values

numInputs = nargin - 2; % a and b are required
inputVar = 1;

while numInputs > 0
    if ~isempty(varargin{inputVar})
        optionals{inputVar} = varargin{inputVar};
    end
    inputVar = inputVar + 1;
    numInputs = numInputs - 1;
end

c = optionals{1};
d = optionals{2};
e = optionals{3};

output = a + b + c + d + e;

This will just add everything together. There is alot of error checking that needs to happen with this. A better approach might be inputParser. This does paired inputs and checking. See Input Parser help

Upvotes: 1

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