[petsc-users] Questions about PCMG
Barry Smith
bsmith at mcs.anl.gov
Tue Apr 3 20:08:27 CDT 2012
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.
>>
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