All calculations were performed using a treecode (Barnes & Hut 1986;
Hernquist 1987, 1990; Dubinski 1988), with a leapfrog timestep 
(corresponding to 
yr when scaled to
physical units for the Galaxy) and a Plummer softening radius
(80 pc). We ran the simulations concurrently on
the Pittsburgh Supercomputing Center CRAY T3D on a 16 node partition.
The San Diego Supercomputing Center Paragon was also used for some
preliminary calculations in a similar manner. Some simulations were
also performed with a completely parallelized treecode (Dubinski
1995).