[petsc-users] Add a matrix to MatNest twice

[Jed Brown]

On Tue, Feb 21, 2012 at 07:43, Thomas Witkowski <
thomas.witkowski at tu-dresden.de> wrote:

> Seems not to work correctly. I made some small changes in
> src/ksp/ksp/examples/tests/ex22.c:
>
> 21c21
> <   np = 2;
> ---
> >   np = 3;
> 62c62
> <   tmp[0][0] = A11;
> ---
> >   tmp[0][0] = A12;
>
> When running with 2 threads, it ends with a segmentation violation. The
> stack is as follows:
>
> [0]PETSC ERROR: [0] MatStashScatterEnd_Private line 109
> src/mat/utils/matstash.c
> [0]PETSC ERROR: [0] MatAssemblyEnd_MPIAIJ line 641
> src/mat/impls/aij/mpi/mpiaij.c
> [0]PETSC ERROR: [0] MatAssemblyEnd line 4934 src/mat/interface/matrix.c
> [0]PETSC ERROR: [0] MatAssemblyEnd_Nest line 228
> src/mat/impls/nest/matnest.c
> [0]PETSC ERROR: [0] MatAssemblyEnd line 4934 src/mat/interface/matrix.c
> [0]PETSC ERROR: [0] test_solve line 17 src/ksp/ksp/examples/tests/ex22.c
>

Okay, the problem is that MatAssemblyBegin and MatAssemblyEnd are called
twice on the same matrix. There are two ways to fix this:

1. Add a flag to Mat so we can tell when a matrix is being assembled. This
makes it so we can't error if an external user leaves a MatAssemblyBegin()
open with no closing MatAssemblyEnd().

2. Uniquify a list of non-empty mats so we only call it once. This doesn't
work because you could have nested MatNests:

[[A 0;0 B] 0; 0 A]


I'm in the midst of something right now, but I'll get back to this if
nobody beats me to it.
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