[ODE] penalty method

[Gary R. Van Sickle]

> Every one say penalty method is bad, but has anybody actually tried it?

I'd wager that pretty much *everybody* has actually tried it.  It's bad.

> I am
> talking about David Wu's gdc talk. Has any one actually implemented his
> method? Not trying to start a fight here, just going through all the
> alternatives...

I don't know what Mr. Wu had to say, but penalty methods have a built-in problem
that is essentially intractable: they, by definition, lead to stiff systems of
differential equations.  Collisions and resting contact are either too squishy
or your simulation blows up or both.

I know for a fact that everybody who's ever considered the rigid-body simulation
problem wish it weren't so, but it is.  And to add insult to injury, the step
from easily-understandable penalty methods to eye-glazingly complex more robust
methods is a very long one.  But luckily, Russ has a good start at putting this
baby to bed once and for all for us ;-).

--
Gary R. Van Sickle
Brewer.  Patriot.