#ident "%W%" %G%
 

The 'flag' demo simulates a cloth in the wind.  The cloth
itself is modeled as a flexable, stretchable surface.
Internal forces keep the cloth together.  External forces
such as the wind, gravity, and the force of the attatchment
points on the poll move and constrain the cloth much in the
same way such forces would act on a real cloth.  It is
the external forces that make it behave like a flag.  By changing
those forces, we could hang curtains, drape table cloths, or even
dress a manikin.

In detail, the cloth is actually represented as a grid of point
masses held together with springs.  These points and springs
follow all of the rules of Newtonian physics, but are otherwise
left alone.  No higher level mathematics need be done to solve
the 'flag equation', because this is a simulation, not just a
graphic representation of a mathematical solution.

