We describe a parallel version of our tree-code for the simulation of
self-gravitating systems in Astrophysics. It is based on a dynamic and adaptive
method for the domain decomposition, which exploits the hierarchical data
arrangement used by the tree-code. It shows low computational costs for the
parallelization overhead -- less than 4% of the total CPU-time in the tests
done -- because the domain decomposition is performed 'on the fly' during the
tree setting and the portion of the tree that is local to each processor
'enriches' itself of remote data only when they are actually needed.
The performances of an implementation of the parallel code on a Cray T3E are
presented and discussed. They exhibit a very good behaviour of the speedup (=15
with 16 processors and 10^5 particles) and a rather low load unbalancing (< 10%
using up to 16 processors), achieving a high computation speed in the forces
evaluation (>10^4 particles/sec with 8 processors).Comment: 10 pages, 8 figures, LaTeX2e, A&A class file needed (included),
submitted to A&A; corrected abstract word wrappin
