An Adaptive Hierarchical Particle‐Mesh Code With Isolated Boundary Conditions

This article describes a new, fully adaptive Particle-Multiple-Mesh numericalsimulation code developed primarily for simulations of small regions (such as agroup of galaxies) in a cosmological context. It integrates the equations ofmotion of a set of particles subject to their mutual gravitational interactionand to an arbitrary external field. The interactions are computed using ahierarchy of nested grids constructed anew at each integration step to enhancethe spatial resolution in high-density regions of interest. Significant efforthas gone into supporting isolated boundary conditions at the top grid level.This makes our method also applicable to non-cosmological problems, at the costof some complications which we discuss. We point out the implications of somedifferences between our approach and those of other authors of similar codes,in particular with respect to the handling of the interface between regions ofdifferent spatial resolution. We present a selection of tests performed toverify the correctness and performance of our implementation. The conclusionsuggests possible further improvements in the areas of independent time stepsand particle softening lengths.Comment: 35 pages, LaTeX, uses aaspp4.sty, 8 figures included ApJ, in press. Only modest changes from earlier posted versio