Two optional parameters mutually exclusive

Hello,

the question is pretty simple. I have a function with two optional parameters:

y = f(x,opt1,opt2)

The user may provide either opt1 or opt2, but not both. In the function, I want to create an array with either lenght opt1 or step size opt2, so the user can only provide one of the optional parameters:

if opt1
  v = linspace(a,b,opt1)
end
if opt2
  v = a:opt2:b
end

How to proceed?

Thank you, Thales

[Adam]

Plenty of acceptable options below. I would hesitate to suggest anything without knowing the usage of the function better. I like Guillaume's answer, but I tend to be fussy about function signatures and like parameters and arguments to be intuitively named so would probably ask the calling function to pass in either 'length' or 'step' rather than 'opt1' or 'opt2'.

But then again that depends on what the calling function 'knows'. It may be that the best solution is for the calling function itself to create the vector v by its chosen method and just pass it in as one single unequivocal argument.

The problem of defining a regular grid, which looks similar to what you are doing, always causes me problems though when I want to define a start and then either a size and an end, a step and an end or a step and a size to parameterise the grid!

Answer 1

[Geoff Hayes]

Thales - you could just pass a structure as the second input to your function, and depending upon which field has been defined, use that to determine what code gets executed (length vs step)

 function y = f(x,params)

 if isfield(params,'opt1')
     v = linspace(a,b,params.opt1);
 elseif isfield(params,'opt2')
     v = a:params.opt2:b;
 end

 % etc.

The function could be called then as

 y=f(42, struct('opt1',102));
 y=f(42, struct('opt2',102));

The structure could be defined before you call the function, or as above.

Answer 2

[Guillaume]

The 'standard' way of doing this in matlab is:

function y = f(x, option, value)
  switch option
    case 'opt1'    %'length' would be a better name
       v = linspace(a,b,value);
    case 'opt2'    %'step' would be a better name
       v = a:value:b;
    otherwise
       error('invalid option name: %s', option);
  end
  %...
end

Answer 3

[Matt J]

How about something like this

     function y = f(x,opt1,opt2)

         if nargin<3,
          opt2=[];
         end

         if nargin<2
          opt1=[];
         end

     if xor(isempty(opt1), isempty(opt2))

        error 'One and only one argument must be empty'

      elseif ~isempty(opt1)
        v = linspace(a,b,opt1)
      elseif ~isempty(opt2)
        v = a:opt2:b
      end