[Yt-dev] Parallel Hop

Stephen Skory stephenskory at yahoo.com
Thu Jan 22 17:26:35 PST 2009


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
________________________________(_)_\(_)_______________



More information about the yt-dev mailing list