[petsc-users] PCMG questions

Tue May 9 21:30:02 CDT 2023

No, there is no DMSHELL.

The code is in adams/snes-example-tokamac: src/dm/impls/plex/tests/ex96.c

With Galerkin coarse grids, the solver does solve but it is wrong so I am
going to focus on that.
I am manually doing what is in DMRefineHierarchy_Plex and there are a few
things that I am not doing.
This code does not work in parallel but I need to redo my MPI syntax
strategy here (building a tree in MPI), so don't look at that.
(the first few coarse grids are attached, wip)

Thanks,
Mark

On Tue, May 9, 2023 at 9:07 PM Barry Smith <bsmith at petsc.dev> wrote:

>
> Must call DMShellSetGlobalVector() or DMShellSetCreateGlobalVector()
> [0]PETSC ERROR: #1 DMCreateGlobalVector_Shell() at
> /Users/markadams/Codes/petsc/src/dm/impls/shell/dmshell.c:210
>
>
>   It looks like you have built a DMSHELL? You need to teach it how to
> generate global vectors since yours currently does not.
>
>   Barry
>
>
> On May 9, 2023, at 5:40 PM, Mark Adams <mfadams at lbl.gov> wrote:
>
>
>
> On Tue, May 9, 2023 at 3:01 PM Barry Smith <bsmith at petsc.dev> wrote:
>
>>
>>
>> On May 9, 2023, at 12:32 PM, Mark Adams <mfadams at lbl.gov> wrote:
>>
>> I have a MG hierarchy that I construct manually with DMRefine and
>> DMPlexExtrude.
>>
>> * The solver works great with chevy/sor but with chevy/sor it converges
>> slowly or I get indefinite PC errors from CG. And the eigen estimates in
>> cheby are really high, like 10-15.
>>
>>
>>    So with Cheby/SOR it works great but with the exact same options
>> Cheby/SOR it behaves poorly? Are you using  some quantum computer and NERSc?
>>
>
> It turned out that I had the sign wrong on my Laplacian point function and
> so the matrix was negative definite. I'm not sure what really happened
> exactly but it is sort of behaving better.
> It looks like my prolongation operator is garbage, the coarse grid
> correction does nothing (cg/jacobi converges in a little less that the
> number of MG iterations times the sum of pre and post smoothing steps), and
> the rows sums of P are not 1.
> Not sure what is going on there, but it is probably related to the DM
> hierarchy not being constructed correctly....
>
>>
>> * I tried turning galerkin=none and I got this error.
>>
>>
>>   This is because without Garkin it needs to restrict the current
>> solution and then compute the coarse grid Jacobian. Since you did not
>> provide a DM that has the ability to even generate coarse grid vectors the
>> process can work. You need a DM that can provide the coarse grid vectors
>> and restrict solutions. Did you forget to pass a DM to the solver?
>>
>
> The DM does everything. Similar to many examples but I've been checking
> with snes/tutorials/ex12.c today.
> I do call:
> PetscCall(DMSetCoarseDM(dmhierarchy[r], dmhierarchy[r-1]));
> But I am missing something else that goes on in DMRefineHierarchy, which I
> can't use because I am semi-coarsening.
> I probably have to build a section on each DM or something, but I have
> bigger fish to fry at this point.
>
> (I construct a 2D coarse grid, refine that a number of times and
> DMPlexExtrude each one the same amount (number and distance), the extruded
> direction is wrapped around a torus and made periodic.
> The fine grid now looks like, and will eventually be, the grids that
> tokamak codes use.)
>
> Thanks,
> Mark
>
>
>>
>> Any thoughts on either of these issues?
>>
>> Thanks,
>> Mark
>>
>> [0]PETSC ERROR: --------------------- Error Message
>> --------------------------------------------------------------
>> [0]PETSC ERROR: Must call DMShellSetGlobalVector() or
>> DMShellSetCreateGlobalVector()
>> [0]PETSC ERROR: WARNING! There are option(s) set that were not used!
>> Could be the program crashed before they were used or a spelling mistake,
>> etc!
>> [0]PETSC ERROR:   Option left: name:-ksp_converged_reason (no value)
>> source: command line
>> [0]PETSC ERROR:   Option left: name:-mg_levels_esteig_ksp_type value: cg
>> source: command line
>> [0]PETSC ERROR:   Option left: name:-mg_levels_pc_type value: sor source:
>> command line
>> [0]PETSC ERROR:   Option left: name:-options_left (no value) source:
>> command line
>> [0]PETSC ERROR: See https://petsc.org/release/faq/ for trouble shooting.
>> [0]PETSC ERROR: Petsc Development GIT revision: v3.19.1-224-g9ed82936d20
>>  GIT Date: 2023-05-07 12:33:48 -0400
>> [0]PETSC ERROR: ./ex96 on a arch-macosx-gnu-O named MarksMac-302.local by
>> markadams Tue May  9 12:26:52 2023
>> [0]PETSC ERROR: Configure options CFLAGS="-g  -Wall" CXXFLAGS="-g  -Wall"
>> COPTFLAGS=-O CXXOPTFLAGS=-O --with-cc=/usr/local/opt/llvm/bin/clang
>> --with-cxx=/usr/local/opt/llvm/bin/clang++ --download-mpich
>> --with-strict-petscerrorcode --download-triangle=1 --with-x=0
>> --with-debugging=0 --download-hdf5=1 PETSC_ARCH=arch-macosx-gnu-O
>> [0]PETSC ERROR: #1 DMCreateGlobalVector_Shell() at
>> /Users/markadams/Codes/petsc/src/dm/impls/shell/dmshell.c:210
>> [0]PETSC ERROR: #2 DMCreateGlobalVector() at
>> /Users/markadams/Codes/petsc/src/dm/interface/dm.c:1022
>> [0]PETSC ERROR: #3 DMGetNamedGlobalVector() at
>> /Users/markadams/Codes/petsc/src/dm/interface/dmget.c:377
>> [0]PETSC ERROR: #4 DMRestrictHook_SNESVecSol() at
>> /Users/markadams/Codes/petsc/src/snes/interface/snes.c:649
>> [0]PETSC ERROR: #5 DMRestrict() at
>> /Users/markadams/Codes/petsc/src/dm/interface/dm.c:3407
>> [0]PETSC ERROR: #6 PCSetUp_MG() at
>> /Users/markadams/Codes/petsc/src/ksp/pc/impls/mg/mg.c:1074
>> [0]PETSC ERROR: #7 PCSetUp() at
>> /Users/markadams/Codes/petsc/src/ksp/pc/interface/precon.c:994
>> [0]PETSC ERROR: #8 KSPSetUp() at
>> /Users/markadams/Codes/petsc/src/ksp/ksp/interface/itfunc.c:406
>> [0]PETSC ERROR: #9 KSPSolve_Private() at
>> /Users/markadams/Codes/petsc/src/ksp/ksp/interface/itfunc.c:824
>> [0]PETSC ERROR: #10 KSPSolve() at
>> /Users/markadams/Codes/petsc/src/ksp/ksp/interface/itfunc.c:1070
>> [0]PETSC ERROR: #11 SNESSolve_KSPONLY() at
>> /Users/markadams/Codes/petsc/src/snes/impls/ksponly/ksponly.c:48
>> [0]PETSC ERROR: #12 SNESSolve() at
>> /Users/markadams/Codes/petsc/src/snes/interface/snes.c:4663
>> [0]PETSC ERROR: #13 main() at ex96.c:433
>>
>>
>>
>>
>>
>
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