NHSE Software Catalog

DIRECT

url

ftp://ftp-hpcc.astro.washington.edu/pub/hpcc/direct.1.1.tar.Z

title_line

an O(N^2) direct sum gravity tool

contact

hpccsoft@astro.washington.edu

version

1.1

abstract

Direct is a tool designed to test more complicated gravity codes such
as Barnes-Hut, Fast Multipole and error-controlling tree-codes as
well as FFT codes in the future (once support for periodic boundary
conditions has been added). It is also the method of choice when
dealing with less than about 10000 particles. The primary application
remains the testing and error analysis of more sophisticated codes.
Typical things looked at in analysis of errors are the distribution of
relative and absolute errors in the acceleration as well as the
maximum and rms values. Another application when a well
understood mass distribution is calculated (such as a king model), is
the analysis of the discreteness noise as a function of N. Direct uses
no approximations in its calculation of the gravitational interaction, it
simply sums over all pairwise interactions. This causes direct to
scale as O(N^2) in CPU time.

keywords

error analysis; cosmology; gravitational interaction

description

http://www-hpcc.astro.washington.edu/tools/