In section 3 we present the result. Section 4 is for discussion.

Model and Numerical method
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Initial models and the system of units
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We followed the evolution of isolated systems of point-mass particles. For all calculations, we used random realizations of the Plummer model as the initial condition. The system of units we adopted is the standard (Heggie) units ([@Heggie1986]), in which $G=1$, $M=1$, and $E=-1/4$, where $G$ is the gravitational constant, $M$ is the total mass of the cluster, and $E$ is the total energy of the cluster. All particles have the same mass $m=1/N$, where $N$ is the total number of particles. In this unit, the half-mass crossing time $t_{hc}$ is $2\sqrt{2}$.

Numerical method
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For all calculations, we used NBODY4 (Aarseth 1985, 1996), modified for GRAPE-4 (Taiji 1996). The numerical integration scheme adopted in NBODY4 is the 4th order Hermite scheme ([@Makino1991a], [@Makino1992]) with the individual (hierarchical) timestep algorithm ([@McMillan1986b], [@Makino1991b]) to use the GRAPE hardware or parallel/vector computers efficiently. Close two-body encounters and stable binaries are handled by KS regularization ([@Kustaanheimo1965]). Special treatment for compact few-body subsystems is also possible.

The 4th-order Hermite scheme has several advantages over traditional ABM type schemes. It is 