[Yt-dev] Parallel Hop

[Matthew Turk]

Hi everyone,

Sorry to pollute the inboxes.  Thing is, I think that maybe I want to
dial back my enthusiasm.  I think what has been sitting poorly with me
is that we don't know *why* the particles are disappearing, and where
they are going.  If they exist within the padding region, then they
should still show up.  I'm going to run some of my own tests on the
RD0005-mine dataset you gave me, Stephen, and see what I come up with.
 I want to figure out *why* it's doing what it's doing.

-Matt

On Thu, Jan 22, 2009 at 5:31 PM, Matthew Turk <matthewturk at gmail.com> wrote:
> Hi Stephen,
>
> Awesome.  I am going to see if I can replicate your methodology over
> here sometime this weekend, because this is great stuff and it should
> get written up.
>
> Looks like basically the entire analysis workflow is now parallelized
> -- derived quantities, projections, halo profiling, radial & phase
> plots, I think even slices, and HOP.  The only major component I see
> as missing is clump finding, and I have an idea for that, but for now
> it should be parallelized on the iterate-over-halos level.
>
> This is tremendous.
>
> -Matt
>
> On Thu, Jan 22, 2009 at 5:26 PM, Stephen Skory <stephenskory at yahoo.com> wrote:
>> All,
>>
>>> 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're interested, I've made a parameter-space survey of processor counts and padding, here, with lots of pictures:
>>
>> http://stephenskory.com/research/?p=1469
>>
>> It's password protected. Contact me off-list if you want it.
>>
>> But in summary, I found that parallel hop differs from serial by no more than 1% in absolute particle count, and the change is larger in smaller haloes, which are already vague to begin with. Even for very large objects (relative to the box) a little bit of padding goes a long way, 0.05 is nearly identical to a padding of 0.2. However, padding is still required to get good answers. The centers change by very, very little between serial and parallel.
>>
>>  _______________________________________________________
>> sskory at physics.ucsd.edu           o__  Stephen Skory
>> http://physics.ucsd.edu/~sskory/ _.>/ _Graduate Student
>> ________________________________(_)_\(_)_______________
>> _______________________________________________
>> Yt-dev mailing list
>> Yt-dev at lists.spacepope.org
>> http://lists.spacepope.org/listinfo.cgi/yt-dev-spacepope.org
>>
>