Gradient field of a Function for 2 Variables

Topic:
Calculus
Task Change the parameters a, b, step and length by using the sliders. Why does the gradient field not change when b is changed? Explore the gradient field of other function, e. g. for f(x,y) = x*y , f(x,y) = sin(x) cos(y) , f(x,y) = 0.5*exp(x)*y etc.