Solving a singular matrix with BoomerAMG

Jed Brown jed at
Thu Nov 5 04:05:26 CST 2009

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.


-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 261 bytes
Desc: OpenPGP digital signature
URL: <>

More information about the petsc-users mailing list