HOP: A New GroupFinding Algorithm for NBody Simulations
Abstract
We describe a new method (HOP) for identifying groups of particles in Nbody simulations. Having assigned to every particle an estimate of its local density, we associate each particle with the densest of the N_{hop} particles nearest to it. Repeating this process allows us to trace a path, within the particle set itself, from each particle in the direction of increasing density. The path ends when it reaches a particle that is its own densest neighbor; all particles reaching the same such particle are identified as a group. Combined with an adaptive smoothing kernel for finding the densities, this method is spatially adaptive, coordinatefree, and numerically straightforward. One can proceed to process the output by truncating groups at a particular density contour and combining groups that share a (possibly different) density contour. While the resulting algorithm has several userchosen parameters, we show that the results are insensitive to most of these, the exception being the outer density cutoff of the groups.
 Publication:

The Astrophysical Journal
 Pub Date:
 May 1998
 DOI:
 10.1086/305535
 arXiv:
 arXiv:astroph/9712200
 Bibcode:
 1998ApJ...498..137E
 Keywords:

 COSMOLOGY: THEORY;
 COSMOLOGY: DARK MATTER;
 METHODS: NUMERICAL;
 Cosmology: Theory;
 Cosmology: Dark Matter;
 Methods: Numerical;
 Astrophysics
 EPrint:
 LaTeX, 18 pages, 7 Postscript figures included. ApJ, in press. Source code available from http://www.sns.ias.edu/~eisenste/hop/hop.html