I would expect 4 calls to MatLUFactorSym here. It looks like the coarse grid is not getting refactored in the second SNES solve.
Are you using Galerkin coarse grids? Perhaps you are not setting a new coarse grid with KSPSetOperator and so MG does not bother refactoring it. Mark On Apr 4, 2012, at 1:53 PM, Yuqi Wu wrote: > Thank you. > > Can I ask another question? > > In my log summary output, it shows that although there are two SNES iteration > and total 9 linear iterations. The functions MatLUFactorSym and > MatLUFactorNum are only called for three times. > > MatLUFactorSym 3 1.0 1.4073e+00 1.0 0.00e+00 0.0 0.0e+00 0.0e+00 > 1.5e+01 1 0 0 0 2 1 0 0 0 2 0 > MatLUFactorNum 3 1.0 3.2754e+01 1.0 9.16e+09 1.0 0.0e+00 0.0e+00 > 0.0e+00 31 97 0 0 0 32 97 0 0 0 280 > > I checked the -info output. It shows that One MatLUFactorSymbolic_SeqAIJ() is > called in down smoother of the first SNES, one MatLUFactorSymbolic_SeqAIJ() > is called in the coarse solve of the first SNES, and one > MatLUFactorSymbolic_SeqAIJ() is called in the down smoother of the second > SNES. > > Do you have any ideas why there are 9 multigrid iterations, but only 3 > MatLUFactorSymbolic calls in the program? > > Best > > Yuqi > > > > > ---- Original message ---- >> Date: Tue, 3 Apr 2012 20:08:27 -0500 >> From: petsc-users-bounces at mcs.anl.gov (on behalf of Barry Smith <bsmith >> at mcs.anl.gov>) >> Subject: Re: [petsc-users] Questions about PCMG >> To: PETSc users list <petsc-users at mcs.anl.gov> >> >> >> There are two linear solves (for 1 SNES and 2 SNES) so there are two >> MGSetUp on each level. Then a total of 9 multigrid iterations (in both >> linear solves together) hence 9 smoother on level 0 (level 0 means coarse >> grid solve). One smooth down and one smooth up on level 1 hence 18 total >> smooths on level 1. 9 computation of residual on level 1 and 18 MgInterp >> because that logs both the restriction to level 0 and the interpolation back >> to level 1 and 18 = 9 + 9. >> >> Barry >> >> On Apr 3, 2012, at 7:57 PM, Yuqi Wu wrote: >> >>> Hi, Barry, >>> >>> Thank you. If my program converges in two SNES iteration, >>> 0 SNES norm 1.014991e+02, 0 KSP its (nan coarse its average), last norm >>> 0.000000e+00 >>> 1 SNES norm 9.925218e-05, 4 KSP its (5.25 coarse its average), last norm >>> 2.268574e-06. >>> 2 SNES norm 1.397282e-09, 5 KSP its (5.20 coarse its average), last norm >>> 1.312605e-12. >>> >>> And -pc_mg_log shows the following output >>> >>> MGSetup Level 0 2 1.0 3.4091e-01 2.1 0.00e+00 0.0 3.0e+02 6.0e+04 >>> 3.0e+01 1 0 3 11 2 1 0 3 11 2 0 >>> MGSmooth Level 0 9 1.0 1.2126e+01 1.0 9.38e+08 3.2 2.8e+03 1.7e+03 >>> 6.4e+02 33 71 28 3 34 35 71 28 3 35 415 >>> MGSetup Level 1 2 1.0 1.3925e-01 2.1 0.00e+00 0.0 1.5e+02 3.1e+04 >>> 2.3e+01 0 0 1 3 1 0 0 1 3 1 0 >>> MGSmooth Level 1 18 1.0 5.8493e+00 1.0 3.66e+08 3.1 1.5e+03 2.9e+03 >>> 3.6e+02 16 28 15 3 19 17 28 15 3 19 339 >>> MGResid Level 1 9 1.0 1.1826e-01 1.4 1.49e+06 2.4 2.0e+02 2.7e+03 >>> 9.0e+00 0 0 2 0 0 0 0 2 0 0 70 >>> MGInterp Level 1 18 1.0 1.2317e-01 1.3 7.74e+05 2.2 3.8e+02 1.1e+03 >>> 1.8e+01 0 0 4 0 1 0 0 4 0 1 37 >>> >>> What are the MGSmooth, MGResid, MGInterp represent for? >>> >>> Best >>> >>> Yuqi >>> >>> ---- Original message ---- >>>> Date: Tue, 3 Apr 2012 19:19:23 -0500 >>>> From: petsc-users-bounces at mcs.anl.gov (on behalf of Barry Smith <bsmith >>>> at mcs.anl.gov>) >>>> Subject: Re: [petsc-users] Questions about PCMG >>>> To: PETSc users list <petsc-users at mcs.anl.gov> >>>> >>>> >>>> -pc_mg_log doesn't have anything to do with DA or DMMG it is part of the >>>> basic PCMG. Are you sure you are calling SNESSetFromOptions()? >>>> >>>> Barry >>>> >>>> On Apr 3, 2012, at 6:56 PM, Yuqi Wu wrote: >>>> >>>>> Hi, Mark, >>>>> >>>>> Thank you so much for your suggestion. >>>>> >>>>> The problem 1 is resolved by avoiding calling PCMGSetNumberSmoothUp. >>>>> >>>>> But since I am using the unstructured grid in my application, I didn't >>>>> use DA or dmmg, so -pc_mg_log didn't give any level information. I try to >>>>> run my code using -info with 1 processor, and I find out some interesting >>>>> issues. >>>> >> >
