The "Constraining Path" window shows the intersection of a green
surface and a red surface. The intersection is colored
blue. A white point is located along this curve and can be
controlled using the variable u0.
The "Constrained Function Values" window shows the values of the
function along the curve. Changing u0 moves the white point along
this curve to help find maximum and minimum values. A readout
gives the value of the function at u0.