CenterStage Object Class:  GradientField
Subclass of:  Arrows
Requires reference to a Surface object

The GradientField class produces a collection of arrows that are the
gradient arrows for a given Surface object.  To make sense, the
surface object should be a function graph (i.e., of the form
z=f(x,y)).  The gradient vectors lie in the xy-plane.  You may want to
use the ArrowScale and ArrowMaxLen directives to make the results
easier to view.

The GradientField class supports all the standard directives, plus the
ArrowHead, ArrowScale, and ArrowMaxLen directives of the Arrow class,
plus the Domain directive of the SurfaceFromSurface class.