  A new, momentum preserving fast Poisson solver for N-body systems sharing
effective O(N) computational complexity, has been recently developed by Dehnen
(2000, 2002). We have implemented the proposed algorithms in a Fortran-90 code,
and parallelized it by a domain decomposition using the MPI routines. The code
has been applied to intensive numerical investigations of galaxy mergers, in
particular focusing on the possible origin of some of the observed scaling
relations of elliptical galaxies. We found that the Fundamental Plane is
preserved by an equal mass merging hierarchy, while it is not in a scenario
where galaxies grow by accretion of smaller stellar systems. In addition, both
the Faber-Jackson and Kormendy relations are not reproduced by our simulations.
