[petsc-users] PCJacobi applied to incompatible vector

Michael Souza souza.michael at gmail.com
Sun Jan 18 06:21:22 CST 2015 

​Thank you for that fast and complete answer.

 sáb, 17 de jan de 2015 21:21, Barry Smith <bsmith at mcs.anl.gov> escreveu:

>
>   As Dave points out the error is not detected because of a confluence of
> options you happen to be using; normally a MatMult() in the Krylov methods
> triggers an error but in your choices there is no MatMult(). The reason
> PCSetUp() and PCSetUp_BJacobi() cannot detect the problem is because they
> may not yet have available the vector that you pass into KSPSolve() hence
> cannot detect the size difference.
>
>     I have added an error check in PCApply() to make sure the sizes of the
> objects passed in are correct; it is in the branch barry/fix-bjacobi-vector-
> lengths and next (I learned my lesson and did not stick it immediately
> into next and master :-(). I've also attached the patch file.
>
>   Thanks
>
>    Barry
>
> [0]PETSC ERROR: --------------------- Error Message
> --------------------------------------------------------------
> [0]PETSC ERROR: Nonconforming object sizes
> [0]PETSC ERROR: Preconditioner number of local rows 20 does not equal
> resulting vector number of rows 30
> [0]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html
> for trouble shooting.
> [0]PETSC ERROR: Petsc Release Version 3.5.2, unknown
> [0]PETSC ERROR: ./ex1 on a arch-maint named Barrys-MacBook-Pro-3.local by
> barrysmith Sat Jan 17 17:15:12 2015
> [0]PETSC ERROR: Configure options --download-mpich --with-fc=0
> --with-cxx=0 --download-sowing=0
> [0]PETSC ERROR: #1 PCApply() line 439 in /Users/barrysmith/Src/petsc/sr
> c/ksp/pc/interface/precon.c
> [0]PETSC ERROR: #2 KSP_PCApply() line 230 in /Users/barrysmith/Src/petsc/
> include/petsc-private/kspimpl.h
> [0]PETSC ERROR: #3 KSPSolve_PREONLY() line 26 in
> /Users/barrysmith/Src/petsc/src/ksp/ksp/impls/preonly/preonly.c
> [0]PETSC ERROR: #4 KSPSolve() line 460 in /Users/barrysmith/Src/petsc/sr
> c/ksp/ksp/interface/itfunc.c
> [0]PETSC ERROR: #5 main() line 59 in /Users/barrysmith/Src/petsc/te
> st-dir/ex1.c
> [0]PETSC ERROR: ----------------End of Error Message -------send entire
> error message to petsc-maint at mcs.anl.gov----------
>
> > On Jan 17, 2015, at 4:13 PM, Dave May <dave.mayhem23 at gmail.com> wrote:
> >
> > Many of the Mat-Vec operations will check that the local and global
> sizes of the matrix and vector are compatible, for example MatMult. If you
> changed your outer KSP type to anything other than PREONLY, an error about
> the mismatched sizes would get thrown.
> >
> > It seems that none of the methods being called from within
> PCSetUp_BJACOBI perform such a check (which is a bit of a surprise). I
> cannot tell you exactly what the result of calling PCApply() with BJACOBI
> will be in the case when the local/global sizes of x,y are larger than the
> those for the operator. (I would guess that the "extra" entries might be
> ignored by PCApply_BJACOBI, but without going through the function in
> detail this really is a guess).
> >
> > The call to PCApply() does not check that the local/global sizes of the
> input and output vectors are compatible with the sizes associated with the
> preconditioned operator. It seems neither does PCSetUp().
> >
> > Shouldn't PCSetUp() perform such a check to detect this error early on
> and to not have the in-built assumption that a method called within
> PCSetUp_XXX() will in fact catch the error??
> >
> >
> > Cheers,
> >   Dave
> >
> >
> >
> > On 17 January 2015 at 22:42, Michael Souza <souza.michael at gmail.com>
> wrote:
> > I'm not sure if this is a bug, but the PCJACOBI can be applied in a
> vector with size different from its operators.
> > In the code below, I define a PCJACOBI for a matrix A with size equal to
> 20 and I apply it in a 30 length vector x.
> >
> > Is this just an unforeseen mistake (unexpected application)? If it
> isn't, what exactly does PCJACOBI do in this situation?
> >
> > Cheers,
> > Michael
> >
> > ------------------------------------------------------------
> -------------------------
> > int main(int argc, char **args){
> >     PetscErrorCode ierr;
> >     PC pc;
> >     KSP ksp;
> >     MPI_Comm comm;
> >     Mat A;
> >     PetscInt i, na=20, nx=30;
> >     Vec x, y;
> >
> >     ierr = PetscInitialize(&argc, &args, (char *) 0, help);
> CHKERRQ(ierr);
> >
> >     // matrix creation and setup
> >     ierr = MatCreate(PETSC_COMM_WORLD, &A); CHKERRQ(ierr);
> >     ierr = MatSetType(A, MATMPIAIJ); CHKERRQ(ierr);
> >     ierr = MatSetSizes(A, PETSC_DECIDE, PETSC_DECIDE, na, na);
> CHKERRQ(ierr);
> >     ierr = MatSetUp(A); CHKERRQ(ierr);
> >     for (i = 0; i < na; i++) {
> >         if(i > 0)
> >             ierr = MatSetValue(A, i, (i - 1), 1.0, INSERT_VALUES);
> CHKERRQ(ierr);
> >         if(i < (na-1))
> >             ierr = MatSetValue(A, i, i+1, 1.0, INSERT_VALUES);
> CHKERRQ(ierr);
> >         ierr = MatSetValue(A, i, i, -2.0, INSERT_VALUES); CHKERRQ(ierr);
> >     }
> >     ierr = MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY); CHKERRQ(ierr);
> >     ierr = MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY); CHKERRQ(ierr);
> >
> >     // vector creation and setup
> >     ierr = VecCreate(PETSC_COMM_WORLD, &x); CHKERRQ(ierr);
> >     ierr = VecSetSizes(x,PETSC_DECIDE,nx);CHKERRQ(ierr);
> >     ierr = VecSetFromOptions(x);CHKERRQ(ierr);
> >     ierr = VecSet(x,1.0);CHKERRQ(ierr);
> >     ierr = VecDuplicate(x,&y);CHKERRQ(ierr);
> >
> >     // set KSP
> >     ierr = PetscObjectGetComm((PetscObject) A, &comm); CHKERRQ(ierr);
> >     ierr = KSPCreate(comm, &ksp); CHKERRQ(ierr);
> >     ierr = KSPSetType(ksp, KSPPREONLY); CHKERRQ(ierr);
> >     ierr = KSPSetOperators(ksp, A, A); CHKERRQ(ierr);
> >     ierr = KSPGetPC(ksp, &pc); CHKERRQ(ierr);
> >     ierr = PCSetType(pc, PCBJACOBI); CHKERRQ(ierr);
> >     ierr = PCSetUp(pc); CHKERRQ(ierr);
> >     { // setup the SubKSP
> >         PetscInt nlocal, dummy;
> >         KSP *subksp;
> >         PC subpc;
> >         ierr = PCBJacobiGetSubKSP(pc, &nlocal, &dummy, &subksp);
> CHKERRQ(ierr);
> >         ierr = KSPSetType(*subksp, KSPPREONLY); CHKERRQ(ierr);
> >         ierr = KSPGetPC(*subksp, &subpc); CHKERRQ(ierr);
> >         ierr = PCSetType(subpc, PCILU); CHKERRQ(ierr);
> >         ierr = PCFactorSetLevels(subpc, 1); CHKERRQ(ierr);
> >         ierr = PCSetFromOptions(subpc); CHKERRQ(ierr);
> >         ierr = PCSetUp(subpc); CHKERRQ(ierr);
> >     }
> >
> >     // solve
> >     ierr = VecView(x,PETSC_VIEWER_STDOUT_WORLD);
> >     ierr = KSPSolve(ksp,x,y); CHKERRQ(ierr);
> >     ierr = VecView(y,PETSC_VIEWER_STDOUT_WORLD); CHKERRQ(ierr);
> >
> >     // destroy objects
> >     ierr = MatDestroy(&A); CHKERRQ(ierr);
> >     ierr = VecDestroy(&x); CHKERRQ(ierr);
> >     ierr = VecDestroy(&y); CHKERRQ(ierr);
> >     ierr = KSPDestroy(&ksp); CHKERRQ(ierr);
> >
> >     return EXIT_SUCCESS;
> > }
> >
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20150118/4dbff428/attachment.html>

More information about the petsc-users mailing list