On Fri, May 15, 2009 at 2:29 PM, Christian May <cmay at phys.ethz.ch> wrote:
> Hi everybody, > > I have trouble solving a linear equation system with PETSc 3.0.0. > I tried the following combinations of solvers and preconditioners and list > the results: > > cg+sor: Linear solve did not converge due to DIVERGED_NAN > cg+bjacobi: Linear solve did not converge due to DIVERGED_INDEFINITE_PC > cg+ilu: Linear solve did not converge due to DIVERGED_INDEFINITE_MAT > 1) This matrix is not SPD > gmres+sor: Linear solve did not converge due to DIVERGED_NAN > gmres+bjacobi:Linear solve did not converge due to DIVERGED_ITS > gmres+ilu: Linear solve did not converge due to DIVERGED_ITS 2) From DIVERGED_NAN, there is either a bug in the code, or you had some sort of floating point badness from excessive iteration. I think the former. 3) Run with -pc_type lu -ksp_type preonly first to test. 4) If you need parallelism with such an ill-conditioned matrix, you can try MUMPS Matt > It might be that the matrix is not positive definite, which explains some > of the problems. In the last two cases it kind of works, but convergence is > horribly slow and it aborts after 10000 iterations. > > If somebody could please have a look at the matrix and the right hand side > vector, I've put them here: > http://www.mayarea.de/download/small_matrix.tgz > The archive contains a file named A.txt, consisting of three columns > i j Aij and a file b.txt with two columns i and bi. > > Any hint on how to solve this linear equation system (in reasonable time) > is appreciated. > > Thanks a lot in advance! > > Christian > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20090515/164859bf/attachment.htm>
