I wont contradict you until we understand each other's terms & accuracy
desires.
again, as I said in a post a while back, for pretty pictures a few thousand
particles are fine, provided you dont go straight Nbody. However, to
self-constently model disk galaxies you need > 10^4 particles per
disk galaxy in order to a) make them stable, and b) keep them dynamically
cool (reference: see Sellwood ARAA a few years back, or, more specifically,
Sellwood, J.A. 1989, \mnras, 238, 115).
If you want to keep disk galaxies cool over more than a few Gyr,
**doing self-consistent (ie no rigid halos, three body models, etc) work**
then you need > 5x10^5 particles.
The post which originally started this thread was (I think) by someone
who wanted to do entry-level exploratory calculations, and as we said
previously, a few thousand particles with tricks such as 3 body will
give nice pictures. but dont trust the detailed dynamics in these
types of simulations -- we find discrepancies in merging times for
galaxies modeled with 5e4 and 5e5 particles.
5e5 particles on a treecode takes ~ 20 Cray C90 hours to run a 1 Gyr
encounter (approx 8 halfmass rotation periods).
so to prb@access2.digex.net, galaxy interactions are in the realm of
current computing power, but you need fast machines (ie, again,
NOT PCs! IBM RS6000s, Dec Alphas, fast Suns, etc. are what you want)
and to chandler@maths.tcd.ie, you're right small nice looking simulations
can be run, but don't trust the detailed dynamics.
> My opinions are wrong? - Well then please send me the correct
> neural net weightings.
"neural net weightings"? i'm just a lowly astronomer, man!
Chris Mihos