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. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120203/6a167d8a/attachment.htm>
