On Wed, Mar 20, 2013 at 3:13 PM, Mehrdad H Farahani <mh.farahani at gmail.com>wrote:
> I am solving a Poisson equation with Neumann boundary conditions applied > along an arbitrary curve using a ghost fluid treatment. The matrix is > non-symmetric and the null space contains more than the constant vector. I > have implemented a solve for the null space itself and have previously > supplied it using MatSetNullSpace. Unfortunately the null space solve is > extremely expensive and does not play well with GAMG or ML. We've checked > that the answers we get without supplying this null space are very close to > the answers we get when we do include it. The matrix for the two solves in > the previous attachment are identical. The problem also seems to be > converging and then suddenly diverges. Is this common behavior for a > singular preconditioner? > If the RHS is not consistent or the preconditioner has a different null space than the operator, you will have problems. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20130320/2c6c73ed/attachment.html>
