I find myself in the position of wanting to minimize a numerical function f(a,b) with respect to a and b for which I do not have a the analytical form f(a,b). All I have is f(a,b) for many values of a and b. Is it still possible to do a gradient descent to minimize f with respect to a and b?
$w_{k+1} = w_{k} - \alpha_{k} \nabla f(w) $
with w the vector holding a and b.
Or is numerical gradient descent impossible?