Thomas Witkowski wrote: > I want so solve a system with a singular matrix (just the laplace > discretized with the fem using pure Neumann boundary conditions) with > BoomerAMG. Is there any way to do it directly in BoomerAMG/PETSc, or > must I change the matrix to make it nonsingular?
The user's manual has a section on solving singular systems, you just need to tell KSP about the null space (either with KSPSetNullSpace or -ksp_constant_null_space). Small known null spaces are rarely an issue with iterative methods. With multigrid, there is some risk that the coarse operator is also singular; this can cause trouble since it is usually solved with a direct solver, but should not happen in your case. Jed -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 261 bytes Desc: OpenPGP digital signature URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20091105/ec2e983d/attachment.pgp>
