If the inputs are effectively constants for a minimization (such as weights that are given for a situation) then they should not form part of x and you should instead parameterize the function call
@(x)objective(x, a, b, c, d)
Where a b c d are the extra inputs
If instead your input x0 values all represent variables whose best value is to be found to minimize the function, then you need to bundle them all together into a single input variable
function cost = objective(allinputs)
a = allinputs(1:4);
b = reshape(allinputs(5:16),4,3);
With x0 = [a0(:) ; b0(:)] ;
