Hi Jed, I've a better understanding now. I think I can use it for my poisson eqn solving which has pressure at the cell center. However, my U and V are staggered. May I right to say that I can still use DA to help the domain spilting process even for this scenario? However, can i solve my momentum eqn with DA still since there's staggering?
Thanks alot! On Fri, Dec 11, 2009 at 7:00 PM, Jed Brown <jed at 59a2.org> wrote: > On Fri, 11 Dec 2009 18:24:58 +0800, Wee-Beng Tay <zonexo at gmail.com> wrote: > > > But you mention abt latency, so shouldn't minimizing the number of > neighbor > > processes reduce latency and improve performance? > > Perhaps, depending on your network. But there are many tricks to hide > latency of ghost updates, global reductions (in dot products) are > harder especially since MPI collectives are synchronous. The higher > iteration counts are way more painful than marginally higher update > cost. > > > For both do u mean dividing 1 big grid into 4 55x35 grids? > > Yes, instead of 4 thin slices. And so on as you refine. DA does this > automatically, just don't choose a prime number of processes (because > then it would be forced into doing slices). > > > so whichever method I use (horizontal or vertical) doesn't matter? But > > splitting to 4 55x35 grids will be better? > > Trying to send directly from some contiguous array is not a worthwhile > optimization. My comment about latency was to guide against another > "optimization" of sending some components of a vector problem separately > when not all components "need" updating (it's likely faster to do one > update of 5 values per ghost node than to do two separate updates of 1 > value per node). > > Splitting into 4 subdomains isn't "better" than 2 subdomains, but when > using many subdomains, they should not be thin slices. > > DA manages all of this. If you have some compelling reason *not* to use > DA, you won't go far wrong by copying the design decisions in DA. > > > Jed > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20091214/d751926c/attachment.htm>
