On Jul 9, 2012, at 3:41 PM, John Mousel wrote: > Can you clarify what you mean by null-space cleaning. I just run SOR on the > coarse grid. >
http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/KSP/KSPSetNullSpace.html#KSPSetNullSpace > > > On Mon, Jul 9, 2012 at 11:52 AM, Mark F. Adams <mark.adams at columbia.edu> > wrote: > > On Jul 9, 2012, at 12:39 PM, John Mousel wrote: > >> Mark, >> >> The problem is indeed non-symmetric. We went back and forth in March about >> this problem. I think we ended up concluding that the coarse size couldn't >> get too small or the null-space presented problems. > > Oh its singular. I forget what the issues were but an iterative coarse grid > solver should be fine for singular problems, perhaps with null space cleaning > if the kernel is sneaking in. Actually there is an SVD coarse grid solver: > > -mg_coarse_pc_type svd > > That is the most robust. > >> When I did get it to work, I tried to scale it up, and on my local >> university cluster, it seemed to just hang when the core counts got above >> something like 16 cores. I don't really trust that machine though. > > That's the machine. GAMG does have some issues but I've not seen it hang. > >> It's new and has been plagued by hardware incompatability issues since day >> 1. I could re-examine this on Kraken. Also, what option are you talking >> about with ML. I thought I had tried all the -pc_ml_CoarsenScheme options, >> but I could be wrong. > > This sounds like the right one. I try to be careful in my solvers to be > invariant to subdomain shapes and sizes and I think Ray Tuminaro (ML > developer) at least has options that should be careful about this also. But > I don't know much about what they are deploying these days. > > Mark > >> >> John >> >> >> >> On Mon, Jul 9, 2012 at 11:30 AM, Mark F. Adams <mark.adams at columbia.edu> >> wrote: >> What problems are you having again with GAMG? Are you problems unsymmetric? >> >> ML has several coarsening strategies available and I think the default does >> aggregation locally and does not aggregate across processor subdomains. If >> you have poorly shaped domains then you want to use a global coarsening >> method (these are not expensive). >> >> Mark >> >> On Jul 9, 2012, at 12:17 PM, John Mousel wrote: >> >>> Mark, >>> >>> I still haven't had much luck getting GAMG to work consistently for my >>> Poisson problem. ML seems to work nicely on low core counts, but I have a >>> problem where I can get long thin portions of grid on some processors >>> instead of nice block like chunks at high core counts, which leads to a >>> pretty tough time for ML. >>> >>> John >>> >>> On Mon, Jul 9, 2012 at 10:58 AM, John Mousel <john.mousel at gmail.com> >>> wrote: >>> Getting rid of the Hypre option seemed to be the trick. >>> >>> On Mon, Jul 9, 2012 at 10:40 AM, Mark F. Adams <mark.adams at columbia.edu> >>> wrote: >>> Google PTL_NO_SPACE and you will find some NERSC presentations on how to go >>> about fixing this. (I have run into these problems years ago but forget >>> the issues) >>> >>> Also, I would try running with a Jacobi solver to see if that fixes the >>> problem. If so then you might try >>> >>> -pc_type gamg >>> -pc_gamg_agg_nsmooths 1 >>> -pc_gamg_type agg >>> >>> This is a built in AMG solver so perhaps it plays nicer with resources ... >>> >>> Mark >>> >>> On Jul 9, 2012, at 10:57 AM, John Mousel wrote: >>> >>> > I'm running on Kraken and am currently working with 4320 cores. I get the >>> > following error in KSPSolve. >>> > >>> > [2711]: >>> > (/ptmp/ulib/mpt/nightly/5.3/120211/mpich2/src/mpid/cray/src/adi/ptldev.c:2046) >>> > PtlMEInsert failed with error : PTL_NO_SPACE >>> > MHV_exe: >>> > /ptmp/ulib/mpt/nightly/5.3/120211/mpich2/src/mpid/cray/src/adi/ptldev.c:2046: >>> > MPIDI_CRAY_ptldev_desc_pkt: Assertion `0' failed. >>> > forrtl: error (76): Abort trap signal >>> > Image PC Routine Line Source >>> > MHV_exe 00000000014758CB Unknown Unknown >>> > Unknown >>> > MHV_exe 000000000182ED43 Unknown Unknown >>> > Unknown >>> > MHV_exe 0000000001829460 Unknown Unknown >>> > Unknown >>> > MHV_exe 00000000017EDE3E Unknown Unknown >>> > Unknown >>> > MHV_exe 00000000017B3FE6 Unknown Unknown >>> > Unknown >>> > MHV_exe 00000000017B3738 Unknown Unknown >>> > Unknown >>> > MHV_exe 00000000017B2B12 Unknown Unknown >>> > Unknown >>> > MHV_exe 00000000017B428F Unknown Unknown >>> > Unknown >>> > MHV_exe 000000000177FCE1 Unknown Unknown >>> > Unknown >>> > MHV_exe 0000000001590A43 Unknown Unknown >>> > Unknown >>> > MHV_exe 00000000014F909B Unknown Unknown >>> > Unknown >>> > MHV_exe 00000000014FF53B Unknown Unknown >>> > Unknown >>> > MHV_exe 00000000014A4E25 Unknown Unknown >>> > Unknown >>> > MHV_exe 0000000001487D57 Unknown Unknown >>> > Unknown >>> > MHV_exe 000000000147F726 Unknown Unknown >>> > Unknown >>> > MHV_exe 000000000137A8D3 Unknown Unknown >>> > Unknown >>> > MHV_exe 0000000000E97BF2 Unknown Unknown >>> > Unknown >>> > MHV_exe 000000000098EAF1 Unknown Unknown >>> > Unknown >>> > MHV_exe 0000000000989C20 Unknown Unknown >>> > Unknown >>> > MHV_exe 000000000097A9C2 Unknown Unknown >>> > Unknown >>> > MHV_exe 000000000082FF2D axbsolve_ 539 >>> > PetscObjectsOperations.F90 >>> > >>> > This is somewhere in KSPSolve. Is there an MPICH environment variable >>> > that needs tweaking? I couldn't really find much on this particular error. >>> > The solver is BiCGStab with Hypre as a preconditioner. >>> > >>> > -ksp_type bcgsl -pc_type hypre -pc_hypre_type boomeramg -ksp_monitor >>> > >>> > Thanks, >>> > >>> > John >>> >>> >>> >> >> > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120710/6dc2a1cd/attachment.html>
