Thank you Barry. In my application, I set the smoothers to be Richardson iteration with ASM preconditioner, and use exact LU in the ASM subdomain solve. And for the coarse solve, I use the GMRES preconditioned ASM solver, again using LU factorization as the subdomain solve.
Yes, there are two different matrices for fine level, but since I am having a coarse grid, it should be two different matrices for coarse level. So I believe it needs 4 LU factorizations. But based on my -info output, it seems only 3 LU factorization are called in the program. I am confused about that. Best Yuqi ---- Original message ---- >Date: Wed, 4 Apr 2012 13:15:45 -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> > > >On Apr 4, 2012, at 12:53 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? > > By default PETSc's multigrid uses ILU smoothing. You can change to SOR with > -mg_levels_pc_type sor > > The factorization only needs to done once then triangular solves (MatSolve) > are done for each smoothing step. Since there are only two different matrices > for the fine level (from the first and second SNES iteration) there only need > to be two factorizations. The smoother is run 9 times because there are 9 > multigrid iterations. > > Barry > >> >> 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. >>>>> >>> >
