In a function with multiple outputs, if one output is empty does that output still need to be calculated within the function?

Say I have a function [a,b] = functionname(c), that looks something like this:

[a,b] = functionname(c)

List of steps to calculate a
List of steps to calculate b (which require a has previously been calculated).

Is there a way to ONLY calculate a? I'm aware that I can type [a,~] = functionname(c), but this will still carry out the list of steps to calculate b (which take a while). I'm looking for something like this:

[a,b] = functionname(c)

List of steps to calculate a

if b is not ~
    List of steps to calculate b
end

However I just can't work out the criteria I'm looking for in the if statement.

I'm aware I could separate this into two functions, and this is the way I'll go about it if what I'm after isn't possible, but I'd like to stick to the one function if possible.

Thanks!

Answer 1

[dpb]

[a,b] = functionname(c)
  List of steps to calculate a
  if nargout > 1
    List of steps to calculate b
  end

doc nargout % and friends and Function descriptive section for details...

Alternatively,

[a,b] = functionname(c)
  List of steps to calculate a
  if nargout==1, return, end  % bail if don't need to compute b
  List of steps to calculate b

NB: nargout also returns 2 for syntax [~,b] = functionname(c); even though there's only one return argument saved; the numbering is length of the list, not actual outputs assigned so above logic is still valid. (Of course, if there were three possible outputs and the call were [~,~,c] = functionname(c); you'd not be able to know that the effort to compute b is futile unless it's as above and c is also dependent upon b.)

[Luke]

Fantastic, nargout does the trick nicely for what I'm after! Like you say, it would be a problem if I was after [~,b] and didn't want to compute a, but in my code I need to calculate a in order to calculate b, so nargout is perfectly fine! Thank you very much!