<scp>exp</scp>: <i>N</i>-body integration using basis function expansions

ABSTRACT We present the N-body simulation techniques implemented in exp code. uses empirically chosen basis functions to expand potential field of an ensemble particles. Unlike other function expansions, derived are adapted input mass distribution, enabling accurate expansion highly non-spherical objects, such as Galactic discs. measure force accuracy three models, one based on a spherical or aspherical halo, exponential disc, and bar-based disc model. find that is direct-summation tree-based calculation, some ways better, while being considerably less computationally intensive. discuss optimizing computation representation. also detail numerical improvements for performing orbit integrations, including time-steps.