A time-reversible, regularized, switching integrator for the N-body problem

This article describes a gravitational N-body integration algorithm conserv ing linear and angular momentum and time-reversal symmetry. Forces are dyna mically partitioned based on interbody separation, so that the long-range f orces are evaluated relatively rarely, and close approaches are treated by an efficient regularization technique. The method incorporates an automatic stepsize adjustment based on a Sundman time-transformation. Although the s cheme is formally second order, the most intensive computations (the close- approach dynamics) are executed at higher order, thus improving the overall accuracy. Numerical experiments indicate that the method can effectively t reat few-body gravitational problems with two-body close approaches, and it compares favorably with other schemes presented in the literature.