  The collapse of non-collisional dark matter and the formation of pancake
structures in the Universe are investigated approximately. Collapse is
described by a system of ordinary differential equations, in the model of a
uniformly rotating, three-axis, uniform density ellipsoid. Violent relaxation,
mass and angular momentum losses are taken into account phenomenologically. The
formation of the equilibrium configuration, secular instability and the
transition from a spheroid to a three-axis ellipsoid are investigated
numerically and analytically in this dynamical model.
