  Adaptive SPH and N-body simulations were carried out to study the evolution
of the equilibrium structure of dark matter halos that result from the
gravitational instability and fragmentation of cosmological pancakes. Such
halos resemble those formed by hierarchical clustering from realistic initial
conditions in a CDM universe and, therefore, serve as a test-bed model for
studying halo dynamics. The dark matter density profile is close to the
universal halo profile identified previously from N-body simulations of
structure formation in CDM, with a total mass and concentration parameter which
grow linearly with scale factor a. When gas is included, this concentration
parameter is slightly larger than the pure N-body result. We also find that the
dark matter velocity distribution is less isotropic and more radial than found
by N-body simulations of CDM.
