[petsc-users] Use boomeramg to solve system of PDEs

[Jed Brown]

On Fri, Feb 3, 2012 at 15:34, Thomas Witkowski <
thomas.witkowski at tu-dresden.de> wrote:

> I did it, but gmres with boomeramg diverges. The system has three unknowns
> per mesh node. Each block operator is either a Laplace or the mass matrix.
> So each block by-itself is solvable with amg. Thus it follows that the
> overall system is solvable? In my case the system is not symmetric and
> indefinite. The boundary conditions are Neuman everywhere, but the global
> matrix has an empty null space. As the local blocks (in the case of the
> discrete Laplace) have constant null space I set -pc_hypre_boomeramg_relax_
> **type_coarse Jacobi for boomeramg not to make direct solves on coarse
> grid. Is there any theoretical reason that AMG cannot work in this case or
> is it a question of just the right settings for the solver?
>

How did you order dofs?

How are the blocks coupled?

AMG is more delicate and generally less robust for systems.
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