  We present a new collapse condition to describe the formation of dark halos
via nonspherical gravitational clustering. This new nonspherical collapse
condition is obtained by the logical generalization of the spherical model to
the nonspherical one. By solving a diffusion-like random matrix equation with
the help of the Monte Carlo method, we show that this nonspherical collapse
condition yields the mass function derived by Sheth & Tormen (1999) which has
been shown to be in excellent agreement with the recent N-body results of high
resolution. We expect that this nonspherical collapse condition might provide
us a deeper insight into the structure formation, and suggest that it should be
widely applied to various cosmological issues such as the galaxy merging
history, the galaxy bias, and so forth.
