Sounds like there are a variable number of inputs to this function. So your function can be used like:
mina = mymin(1,2,3,4,5); % five inputs
minb = mymin(4.5,9,3); % three inputs
If that is the case, then you want to use the varargin (variable arguments in) input variable in your function signature:
function minval = mymin(varargin)
% varargin is a cell array
The number of arguments in, nargin, is something you can use in your function body to indicate how many inputs have been passed to your function. Try the above and see what happens.
