On Dec 11, 2012, at 10:00 AM, Daniel Arndt <daniel.arndt at stud.uni-goettingen.de> wrote:
> Thank you Barry for your suggestions. > > The error I get is now KSP_DIVERGED_INDEFINITE_PC. The matrix that I try to > invert is actually symmetric and positive definite. I was not aware that this > can lead to a indefinite preconditioner. Absolutely. Many preconditioners do not retain this feature even in exact precision and with numerical effects it can even appear unexpected. By default BoomAMG doesn't retain this. > If I use a Jacobi preconditioner or tell BoomerAMG that the matrix is > symmetric I don't encounter any errors. So I'm quite for now :-) > > Daniel >> Daniel, >> >> That message is not coming from PETSc so likely Deal.II is processing >> the result from KSPConvergedReason() and generating that less then totally >> useful output. If you run with -ksp_converged_reason PETSC will (if Deal.II >> processes PETSc options correctly) print a more complete reason. >> >> Off hand I am guessing that CG detected a non-symmetric or indefinite >> matrix or preconditioner which it cannot handle so it barfed out. You can >> run with GMRES instead of CG and if that converges then this is the likely >> explanation. >> >> Barry >> >> >> On Dec 11, 2012, at 8:19 AM, Daniel Arndt < >> daniel.arndt at stud.uni-goettingen.de >> > wrote: >> >> > >> Hello everyone, >> >> > >> >> >> > >> at the moment I'm trying to solve a Poisson problem with SIPG >> >> > >> stabilization and discontinuous finite elements. The matrix is >> >> > >> constructed in deal.II. When I try to solve this problem with PETSc's CG >> >> > >> solver and a BlockJacobi preconditioner or a BoomerAMG preconditioner >> >> > >> from the Hypre package I get this weird error message. >> >> > >> >> >> > >> Exception on processing: >> >> > >> Iterative method reported convergence failure in step 3 with residual >> >> > >> 1.50616 >> >> > >> Aborting! >> >> > >> >> >> > >> Since the solver is allowed to take 5000 steps this convergence failure >> >> > >> is clearly early. Did anyone encounter such an error before? What can >> >> > >> produce such an early convergence failure? >> >> > >> >> >> > >> Thanks in advance, >> >> > >> Daniel >> >> > >> >> >> > >> >> >> > >> >> >>
