Galaxy dynamics by N-body simulation

I compare various popular and unpopular techniques for simulating large collisionless stellar systems. I give a quantitative comparison of the raw cpu times required for ve separate codes, including tree codes and basis function expansions, which demonstrate that grid codes are most eecient for large numbers of particles. Since eeciency is only one consideration when choosing a code, I discuss other strengths and weaknesses of the various methods. While some applications may require the maximum possible number of particles, I argue that quiet start techniques can often permit reliable results to be obtained with moderate particle numbers. I suggest a quiet start procedure for spherical stellar systems and show that it leads to a signiicant reduction in the relaxation rate. The combination of eecient codes and quiet starts allows many galactic dynamical problems to be tackled without the need for supercomputers.