[petsc-users] GMRES -> PCMG -> PCASM pre- post- smoother
Lorenzo Alessio Botti
lorenzoalessiobotti at gmail.com
Thu Aug 20 07:57:38 CDT 2015
I guess that only one memory allocation is done, but basically this is what I’m asking as well.
Is this correct? I’d be more confident if one of the developers confirmed this.
Lorenzo
> On 20 Aug 2015, at 14:00, Aulisa, Eugenio <eugenio.aulisa at ttu.edu> wrote:
>
> Thanks Lorenzo
>
> If I well understood what you say is
>
> Set up PCASM for the smoother_down[i] and then
> feed it up to smoother_up[i]
>
> Does this assure that only one
> memory allocation is done for PCASM?
>
>
> Eugenio
> From: Lorenzo Alessio Botti [lorenzoalessiobotti at gmail.com]
> Sent: Thursday, August 20, 2015 5:29 AM
> To: petsc-users at mcs.anl.gov
> Cc: Aulisa, Eugenio
> Subject: GMRES -> PCMG -> PCASM pre- post- smoother
>
> I tried to achieve this behaviour getting all the smothers and setting the same preconditioner to the down and up smoother on the same level.
>
>
> smoothers.resize(nLevels+1);
> smoothers_up.resize(nLevels);
> for (PetscInt i = 0; i < nLevels; i++)
> {
> PCMGGetSmootherDown(M_pc,nLevels-i,&(smoothers[i]));
> KSPSetInitialGuessNonzero(smoothers[i],PETSC_TRUE); // for full and wCicle
> PCMGGetSmootherUp(M_pc,nLevels-i,&(smoothers_up[i]));
> }
> PCMGSetNumberSmoothDown(M_pc,1);
> PCMGSetNumberSmoothUp(M_pc,1);
>
> … set coarse solver options here
>
> for (PetscInt i = 0; i < nLevels; i++)
> {
> PC pc;
> KSPSetType(smoothers[i], KSPGMRES);
> KSPGetPC(smoothers[i], &pc);
> KSPSetPCSide(smoothers[i], PC_RIGHT);
> PCSetType(pc, PCASM);
> PCFactorSetPivotInBlocks(pc, PETSC_TRUE);
> PCFactorSetAllowDiagonalFill(pc);
> PCFactorSetReuseFill(pc, PETSC_TRUE);
> PCFactorSetReuseOrdering(pc, PETSC_TRUE);
> KSPSetType(smoothers_up[i], KSPGMRES);
> KSPSetPC(smoothers_up[i], pc);
> KSPSetPCSide(smoothers_up[i], PC_RIGHT);
> KSPSetConvergenceTest(smoothers[i],KSPConvergedSkip,NULL,NULL);
> KSPSetConvergenceTest(smoothers_up[i],KSPConvergedSkip,NULL,NULL);
> KSPSetNormType(smoothers[i],KSP_NORM_NONE);
> KSPSetNormType(smoothers_up[i],KSP_NORM_NONE);
> }
>
> Is this correct?
> Note moreover that for Full Multigrid and W cicles to work as expected I need to add the KSPSetInitialGuessNonZero option.
>
> Bests
> Lorenzo
>
>> Message: 4
>> Date: Thu, 20 Aug 2015 02:37:13 -0500
>> From: Barry Smith <bsmith at mcs.anl.gov <mailto:bsmith at mcs.anl.gov>>
>> To: "Aulisa, Eugenio" <eugenio.aulisa at ttu.edu <mailto:eugenio.aulisa at ttu.edu>>
>> Cc: "petsc-users at mcs.anl.gov <mailto:petsc-users at mcs.anl.gov>" <petsc-users at mcs.anl.gov <mailto:petsc-users at mcs.anl.gov>>
>> Subject: Re: [petsc-users] GMRES -> PCMG -> PCASM pre- post- smoother
>> Message-ID: <1CF3ABE1-214C-4BBC-B8FF-93416EC26EFC at mcs.anl.gov <mailto:1CF3ABE1-214C-4BBC-B8FF-93416EC26EFC at mcs.anl.gov>>
>> Content-Type: text/plain; charset="us-ascii"
>>
>>
>> What you describe is not the expected behavior. I expected exactly the result that you expected.
>>
>> Do you perhaps have some PETSc options around that may be changing the post-smoother? On the command line or in the file petscrc or in the environmental variable PETSC_OPTIONS? Can you send us some code that we could run that reproduces the problem?
>>
>> Barry
>>
>>> On Aug 19, 2015, at 9:26 PM, Aulisa, Eugenio <eugenio.aulisa at ttu.edu <mailto:eugenio.aulisa at ttu.edu>> wrote:
>>>
>>> Hi,
>>>
>>> I am solving an iteration of
>>>
>>> GMRES -> PCMG -> PCASM
>>>
>>> where I build my particular ASM domain decomposition.
>>>
>>> In setting the PCMG I would like at each level
>>> to use the same pre- and post-smoother
>>> and for this reason I am using
>>> ...
>>> PCMGGetSmoother ( pcMG, level , &subksp );
>>>
>>> to extract and set at each level the ksp object.
>>>
>>> In setting PCASM then I use
>>> ...
>>> KSPGetPC ( subksp, &subpc );
>>> PCSetType ( subpc, PCASM );
>>> ...
>>> and then set my own decomposition
>>> ...
>>> PCASMSetLocalSubdomains(subpc,_is_loc_idx.size(),&_is_ovl[0],&_is_loc[0]);
>>> ...
>>>
>>> Now everything compiles, and runs with no memory leakage,
>>> but I do not get the expected convergence.
>>>
>>> When I checked the output of -ksp_view, I saw something that puzzled me:
>>> at each level >0, while in the MG pre-smoother the ASM domain decomposition
>>> is the one that I set, for example with 4 processes I get
>>>
>>>>>>>>>>>>>>>>>>>>>>
>>> ...
>>> Down solver (pre-smoother) on level 2 -------------------------------
>>> KSP Object: (level-2) 4 MPI processes
>>> type: gmres
>>> GMRES: restart=30, using Classical (unmodified) Gram-Schmidt Orthogonalization with no iterative refinement
>>> GMRES: happy breakdown tolerance 1e-30
>>> maximum iterations=1
>>> using preconditioner applied to right hand side for initial guess
>>> tolerances: relative=1e-12, absolute=1e-20, divergence=1e+50
>>> left preconditioning
>>> using nonzero initial guess
>>> using NONE norm type for convergence test
>>> PC Object: (level-2) 4 MPI processes
>>> type: asm
>>> Additive Schwarz: total subdomain blocks = 198, amount of overlap = 0
>>> Additive Schwarz: restriction/interpolation type - RESTRICT
>>> [0] number of local blocks = 52
>>> [1] number of local blocks = 48
>>> [2] number of local blocks = 48
>>> [3] number of local blocks = 50
>>> Local solve info for each block is in the following KSP and PC objects:
>>> - - - - - - - - - - - - - - - - - -
>>> ...
>>>>>>>>>>>>>>
>>>
>>>
>>> in the post-smoother I have the default ASM decomposition with overlapping 1:
>>>
>>>
>>>>>>>>>>>>>>
>>> ...
>>> Up solver (post-smoother) on level 2 -------------------------------
>>> KSP Object: (level-2) 4 MPI processes
>>> type: gmres
>>> GMRES: restart=30, using Classical (unmodified) Gram-Schmidt Orthogonalization with no iterative refinement
>>> GMRES: happy breakdown tolerance 1e-30
>>> maximum iterations=2
>>> tolerances: relative=1e-12, absolute=1e-20, divergence=1e+50
>>> left preconditioning
>>> using nonzero initial guess
>>> using NONE norm type for convergence test
>>> PC Object: (level-2) 4 MPI processes
>>> type: asm
>>> Additive Schwarz: total subdomain blocks = 4, amount of overlap = 1
>>> Additive Schwarz: restriction/interpolation type - RESTRICT
>>> Local solve is same for all blocks, in the following KSP and PC objects:
>>> KSP Object: (level-2sub_) 1 MPI processes
>>> type: preonly
>>> maximum iterations=10000, initial guess is zero
>>> tolerances: relative=1e-05, absolute=1e-50, divergence=10000
>>> left preconditioning
>>> ...
>>>>>>>>>>>>>>>>
>>> %%%%%%%%%%%%%%%%%%%%%%%%
>>>
>>> So it seams that by using
>>>
>>> PCMGGetSmoother ( pcMG, level , &subksp );
>>>
>>> I was capable to set both the pre- and post- smoothers to be PCASM
>>> but everything I did after that applied only to the
>>> pre-smoother, while the post-smoother got the default PCASM options.
>>>
>>> I know that I can use
>>> PCMGGetSmootherDown and PCMGGetSmootherUp, but that would
>>> probably double the memory allocation and the computational time in the ASM.
>>>
>>> Is there any way I can just use PCMGGetSmoother
>>> and use the same PCASM in the pre- and post- smoother?
>>>
>>> I hope I was clear enough.
>>>
>>> Thanks a lot for your help,
>>> Eugenio
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