[Yt-dev] Parallel Hop

[Brian O'Shea]

>> I was wondering how parallel HOP is going?  I've got some big datasets
>> I'd like to run it on, but I haven't heard if it's working as expected
>> or not.  What's the current status?  Are the results converged?  Do we
>> have a good idea of how to pad the tiles?
>
> I got distracted from some of my testing (sorry!), and so my opinions aren't fully set yet. I'd say for now if you give a
> 'healthy' amount of padding, so larger than your largest object, you can do science with it right now. The changes between
> serial and parallel HOP are smaller than the fuzziness of halo boundaries themselves, so go with it!

Could you quantify that a bit, Stephen?  I definitely agree with the
point about the fuzziness of halo boundaries, but how far off are the
results when you vary processor count?  If you were to make halo
catalogs of the same dataset using 1,2,4,8, etc. processors, and then
compare them (assuming that n=1 processor is the "perfect" solution),
how far off are the halo centers?

If you haven't done this particular comparison, I'm happy to do it.  I
have some code laying around from the Enzo/Gadget code comparison that
would be perfect for this task, if you want to generate the halo
catalogs and give 'em to me.

--Brian