What specifically do you mean when you say argmin?
Do you mean the location of the minimum element in a vector? See the second output of the min function.
Do you mean the number of inputs with which the live function was called? I believe nargin and narginchk both work inside a live function.
Do you mean a value that minimizes the live function? Call fminsearch or fmincon with a handle to your live function as input.
If you mean something else, please clarify.