We present results on numerical integrators that
exactly preserve
momentum maps and Poisson brackets, thereby inducing integrators that
preserve the natural Lie-Poisson structure on the duals of the Lie algebras.
The techniques are based on time-stepping with the generating function
obtained as an approximate solution to the Hamilton Jacobi equation, following
ideas of de Vogelaére, Channel, and Feng. To accomplish this, the
Hamilton-Jacobi theory is reduced from
J*G to
, where
is the Lie algebra of a Lie group
G. The algorithms exactly
preserve any additional conserved quantities in the problem. An explicit
algorithm is given for any semi-simple group and in particular for the
Euler equation of rigid body dynamics.