[petsc-users] multigrid implementation problem

[Jed Brown]

On Sun, Jun 10, 2012 at 8:32 PM, Nakib Haider Protik <nprot048 at uottawa.ca>wrote:

> Here's the code with the changes you suggested followed by the terminal
> output:
>
>    KSPCreate(PETSC_COMM_WORLD, &ksp);
>    //KSPCreate(PETSC_COMM_WORLD, &cksp);
>    //KSPCreate(PETSC_COMM_WORLD, &uksp);
>    //KSPCreate(PETSC_COMM_WORLD, &dksp);
>
>    //KSPSetType(ksp, KSPGMRES);
>    //KSPSetType(cksp, KSPGMRES);
>    //KSPSetType(uksp, KSPGMRES);
>    //KSPSetType(dksp, KSPGMRES);
>
>    KSPGetPC(ksp, &pc);
>    //KSPGetPC(cksp, &pc);
>    //KSPGetPC(uksp, &pc);
>    //KSPGetPC(dksp, &pc);
>
>    KSPSetFromOptions(ksp);
>
>    PCSetType(pc, PCMG);
>    PCMGSetLevels(pc, 2, PETSC_NULL);
>    PCMGSetType(pc, PC_MG_MULTIPLICATIVE);
>    PCMGSetCycleType(pc, PC_MG_CYCLE_V);
>    MatDuplicate(A, MAT_COPY_VALUES, &P);
>    PCMGSetCyclesOnLevel(pc, 0, 1);
>    PCMGSetCyclesOnLevel(pc, 1, 1);
>
>     //PCMGGetCoarseSolve(pc, &cksp);
>    //PCMGGetSmootherDown(pc, 0,  &dksp);
>    //PCMGGetSmootherUp(pc, 1, &uksp);
>
>    PCMGSetInterpolation(pc, 1, P);
>    PCMGSetRestriction(pc, 1, P);
>    PCMGSetResidual(pc, 0, PCMGDefaultResidual, P);
>    PCMGSetResidual(pc, 1, PCMGDefaultResidual, P);
>

^^ I already explained that these lines are semantically incorrect. You are
using the matrix P in different places that do not make sense.

You have not set an operator for the smoother and you haven't set a vector.
You have to do at least one of those if you want to use the "advanced" PCMG
interface.


Before trying anything else, install petsc-3.3 and read through this
example.

http://www.mcs.anl.gov/petsc/petsc-current/src/ksp/ksp/examples/tutorials/ex45.c.html

Compile it and run it with

./ex45 -da_refine 3 -ksp_monitor -pc_type mg -ksp_view

Read through the output and understand what algorithm it is using.

Run with -help and look at the options starting with "-pc_mg" and
"-mg_levels".

Change the algorithm using command line parameters.

Then, and only then, consider using the low-level PCMG interface directly.


>
>     KSPSetOperators(ksp, A, P, SAME_NONZERO_PATTERN);
>    KSPSolve(ksp, breal, xreal_harm);
>    KSPSolve(ksp, bimag, ximag_harm);
>
> [0]PETSC ERROR: --------------------- Error Message
> ------------------------------------
> [0]PETSC ERROR: Null argument, when expecting valid pointer!
> [0]PETSC ERROR: Null Object: Parameter # 1!
> [0]PETSC ERROR:
> ------------------------------------------------------------------------
> [0]PETSC ERROR: Petsc Release Version 3.0.0, Patch 12, Tue Mar 16 23:20:08
> CDT 2010
>

I have asked you several times to upgrade to petsc-3.3. Please do that now,
before you write back to this list.



> [0]PETSC ERROR: See docs/changes/index.html for recent updates.
> [0]PETSC ERROR: See docs/faq.html for hints about trouble shooting.
> [0]PETSC ERROR: See docs/index.html for manual pages.
> [0]PETSC ERROR:
> ------------------------------------------------------------------------
> [0]PETSC ERROR: ./3dPoissonSolver-cyl-test on a linux-gnu named nakib-F82Q
> by nakib Sun Jun 10 21:30:04 2012
> [0]PETSC ERROR: Libraries linked from
> /home/nakib/petsc-3.0.0-p12/linux-gnu-c-debug/lib
> [0]PETSC ERROR: Configure run at Wed May  9 13:44:03 2012
> [0]PETSC ERROR: Configure options --with-cc=gcc --with-fc=gfortran
> --download-f-blas-lapack=1 --download-mpich=1 --with-shared=0
> [0]PETSC ERROR:
> ------------------------------------------------------------------------
> [0]PETSC ERROR: MatGetVecs() line 7098 in src/mat/interface/matrix.c
> [0]PETSC ERROR: KSPGetVecs() line 820 in src/ksp/ksp/interface/iterativ.c
> [0]PETSC ERROR: PCSetUp_MG() line 465 in src/ksp/pc/impls/mg/mg.c
> [0]PETSC ERROR: PCSetUp() line 794 in src/ksp/pc/interface/precon.c
> [0]PETSC ERROR: KSPSetUp() line 237 in src/ksp/ksp/interface/itfunc.c
> [0]PETSC ERROR: KSPSolve() line 353 in src/ksp/ksp/interface/itfunc.c
> [0]PETSC ERROR: --------------------- Error Message
> ------------------------------------
> [0]PETSC ERROR: Null argument, when expecting valid pointer!
> [0]PETSC ERROR: Null Object: Parameter # 1!
> [0]PETSC ERROR:
> ------------------------------------------------------------------------
> [0]PETSC ERROR: Petsc Release Version 3.0.0, Patch 12, Tue Mar 16 23:20:08
> CDT 2010
> [0]PETSC ERROR: See docs/changes/index.html for recent updates.
> [0]PETSC ERROR: See docs/faq.html for hints about trouble shooting.
> [0]PETSC ERROR: See docs/index.html for manual pages.
> [0]PETSC ERROR:
> ------------------------------------------------------------------------
> [0]PETSC ERROR: ./3dPoissonSolver-cyl-test on a linux-gnu named nakib-F82Q
> by nakib Sun Jun 10 21:30:04 2012
> [0]PETSC ERROR: Libraries linked from
> /home/nakib/petsc-3.0.0-p12/linux-gnu-c-debug/lib
> [0]PETSC ERROR: Configure run at Wed May  9 13:44:03 2012
> [0]PETSC ERROR: Configure options --with-cc=gcc --with-fc=gfortran
> --download-f-blas-lapack=1 --download-mpich=1 --with-shared=0
> [0]PETSC ERROR:
> ------------------------------------------------------------------------
> [0]PETSC ERROR: MatGetVecs() line 7098 in src/mat/interface/matrix.c
> [0]PETSC ERROR: KSPGetVecs() line 820 in src/ksp/ksp/interface/iterativ.c
> [0]PETSC ERROR: PCSetUp_MG() line 465 in src/ksp/pc/impls/mg/mg.c
> [0]PETSC ERROR: PCSetUp() line 794 in src/ksp/pc/interface/precon.c
> [0]PETSC ERROR: KSPSetUp() line 237 in src/ksp/ksp/interface/itfunc.c
> [0]PETSC ERROR: KSPSolve() line 353 in src/ksp/ksp/interface/itfunc.c
>
> The code converges to the wrong solution too.
>

The error above is fatal, the solver is not configured correctly. You are
supposed to catch the error (you can use the CHKERRQ macro).
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