[petsc-dev] FieldSplit with different nonzero pattern

[Pierre Jolivet]

Hong,
Thanks for your reply.
It’s not so minimalist, but at least it is based on one of your example.
diff --git a/src/ksp/ksp/examples/tutorials/ex42.c b/src/ksp/ksp/examples/tutorials/ex42.c
index 8be4389a2d..520c82569a 100644
--- a/src/ksp/ksp/examples/tutorials/ex42.c
+++ b/src/ksp/ksp/examples/tutorials/ex42.c
@@ -1953,6 +1953,15 @@ static PetscErrorCode solve_stokes_3d_coupled(PetscInt mx,PetscInt my,PetscInt m
     }
   }
   ierr = KSPSolve(ksp_S,f,X);CHKERRQ(ierr);
+  PetscViewerPushFormat(PETSC_VIEWER_STDOUT_WORLD, PETSC_VIEWER_ASCII_INFO);
+  MatView(A, PETSC_VIEWER_STDOUT_WORLD);
+  Mat C;
+  MatMatMult(A, A, MAT_INITIAL_MATRIX, PETSC_DEFAULT, &C);
+  MatView(C, PETSC_VIEWER_STDOUT_WORLD);
+  PetscViewerPopFormat(PETSC_VIEWER_STDOUT_WORLD);
+  ierr = KSPSetOperators(ksp_S,C,C);CHKERRQ(ierr);
+  ierr = KSPSolve(ksp_S,f,X);CHKERRQ(ierr);
+  MatDestroy(&C);

   ierr = PetscOptionsGetBool(NULL,NULL,"-write_pvts",&write_output,NULL);CHKERRQ(ierr);
   if (write_output) {ierr = DAView3DPVTS(da_Stokes,X,"up");CHKERRQ(ierr);}

$ mpirun -np 1 ./ex42 -mx 2 -my 2 -mz 2 -stokes_pc_type fieldsplit
This should give you this exact error.
Do you know of a way to bypass the error by flushing/destroying the PC while still keeping the options for the following KSPSolve?

Thanks in advance,
Pierre

> On 3 May 2018, at 5:07 PM, Hong <hzhang at mcs.anl.gov> wrote:
> 
> Pierre :
> The code crashes inside
> if (scall == MAT_REUSE_MATRIX) {
> ...
> } 
> which assumes both original matrix and its submatrices data structures remain unchanged.
> We did not anticipate the usage of looping
> 
> 3) change the sparsity pattern of the Mat for one of the field
> 4) do a KSPSolve
>  
> Can you send us a stand-alone code for this type of application.
> We will investigate how to support it.
> 
> Hong
> 
> I cannot change this calling sequence, because I’d like to nest 3) and 4) inside a loop.
> However, I end up with this error during 4):
> [0]PETSC ERROR: Nonconforming object sizes
> [0]PETSC ERROR: Cannot reuse matrix. wrong no of nonzeros
> [0]PETSC ERROR: Petsc Development GIT revision: v3.9-13-g05d412bc58  GIT Date: 2018-04-09 08:39:52 -0500
> 
> [0]PETSC ERROR: #1 MatCreateSubMatrix_SeqAIJ() line 2330 in /Users/jolivet/Documents/repositories/petsc/src/mat/impls/aij/seq/aij.c
> [0]PETSC ERROR: #2 MatCreateSubMatrix_MPIAIJ_SameRowColDist() line 3184 in /Users/jolivet/Documents/repositories/petsc/src/mat/impls/aij/mpi/mpiaij.c
> [0]PETSC ERROR: #3 MatCreateSubMatrix_MPIAIJ() line 3310 in /Users/jolivet/Documents/repositories/petsc/src/mat/impls/aij/mpi/mpiaij.c
> [0]PETSC ERROR: #4 MatCreateSubMatrix() line 7813 in /Users/jolivet/Documents/repositories/petsc/src/mat/interface/matrix.c
> [0]PETSC ERROR: #5 PCSetUp_FieldSplit() line 564 in /Users/jolivet/Documents/repositories/petsc/src/ksp/pc/impls/fieldsplit/fieldsplit.c
> [0]PETSC ERROR: #6 PCSetUp() line 923 in /Users/jolivet/Documents/repositories/petsc/src/ksp/pc/interface/precon.c
> [0]PETSC ERROR: #7 PCApply() line 453 in /Users/jolivet/Documents/repositories/petsc/src/ksp/pc/interface/precon.c
> [0]PETSC ERROR: #8 KSP_PCApply() line 276 in /Users/jolivet/repo/petsc/include/petsc/private/kspimpl.h
> [0]PETSC ERROR: #9 KSPFGMRESCycle() line 166 in /Users/jolivet/Documents/repositories/petsc/src/ksp/ksp/impls/gmres/fgmres/fgmres.c
> [0]PETSC ERROR: #10 KSPSolve_FGMRES() line 291 in /Users/jolivet/Documents/repositories/petsc/src/ksp/ksp/impls/gmres/fgmres/fgmres.c
> [0]PETSC ERROR: #11 KSPSolve() line 669 in /Users/jolivet/Documents/repositories/petsc/src/ksp/ksp/interface/itfunc.c
> 
> Is this the expected behaviour? Would you need a MWE?
> What I find funny is that if I turn -info on, then just before the error, I get:
> [0] PCSetUp(): Setting up PC with different nonzero pattern
> So why is it trying to reuse the matrix? I am missing a call to some function?
> 
> Thanks in advance,
> Pierre
> 

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