[ODE] solving penetrations "statically"

[Erin Catto]

If you know that everything should be at rest, you can set the velocities to
zero after each time step. 

Otherwise, you'll need to compute two sets of Lagrange multipliers
(lambdas). The first set includes the position correction while the second
set does not. Apply the first set to generate non-persistant velocities that
are simply used to update the positions. Use the second set of lambdas to
generate the final velocities for the step. This way position correction
won't affect the momentum of the system.
 
Erin