This demo opens with one window titled "Constraining Surface".
Modify this surface by modifying the equation in this window.
Several intervals have been included in the control window to make
modifying this surface easier. The white hotspot is restricted to
this surface. Enter your desired function of three variables, and
observe the readout telling you the value of the function at the
hotspot restrained to the surface. Try to find maximum and
minimum values for locations of the hotspot on the surface.