[petsc-users] GAMG

[Jeremy Theler]

Hi Mark.

The matrix is solved well with lu/preonly.

If I do not call PCSetCoordinates() the error goes away but convergence
is slow.

I call PCSetCoordinates() this way (1 processor):

    PetscMalloc1(dimensions * mesh->n_nodes, &coords);
    for (j = 0; j < mesh->n_nodes; j++) {
      for (d = 0; d < dimensions; d++) {
        coords[j*dimensions + d] = mesh->node[j].x[d];
      }
    }
    PCSetCoordinates(pc, dimensions, dimensions * mesh->n_nodes,
coords);
    PetscFree(coords);


Thanks
--
jeremy



On Fri, 2016-10-28 at 09:16 -0400, Mark Adams wrote:
> I think there is something wrong with your matrix. Use any solver and
> verify that you like the solution first.
> 
> On Fri, Oct 28, 2016 at 9:13 AM, Jeremy Theler <jeremy at seamplex.com>
> wrote:
>         Hi! I want to use PCGAMG as a preconditioner for a 3D linear
>         elasticity
>         problem (displacement-based FEM formulation) over an
>         unstructured grid.
>         I am not using DMPlex, I just build the stiffness matrix
>         myself and pass
>         it to PETSc.
>         
>         I set MatSetBlockSize() to 3 and pass the node coordinates
>         through
>         PCSetCoordinates(). But using gamg and gmres I get:
>         
>         PETSc error 77-0 'Eigen estimator failed: DIVERGED_NANORINF at
>         iteration
>         0'
>         in /home/gtheler/libs/petsc-3.7.4/src/ksp/ksp/impls/cheby/cheby.c
>         KSPSolve_Chebyshev:440
>         
>         Any suggestion? Another PC/KSP combination to try?
>         
>         Thanks
>         --
>         jeremy
>         
>         
> 
>