Efficient Scheme for Active Particle Selection in N-body Simulations

We propose an efficient method for active particle selection, working with Hermite Individual Time Steps (HITS) scheme in direct N-body simulation code φGRAPE . For a simulation with N particles, this method can reduce the computation complexity of active particle selection, from O(N ·Nstep) to O(Nact ·Nstep), where Nact is the average active particle number in every time step which is much less than N and Nstep is the total time steps integrated during the simulation. Thus can save a lot of time spend on active particle selection part, especially in the case of low Nact. Subject headings: computation algorithm