On Fri, Aug 17, 2012 at 3:10 AM, Thomas Witkowski < thomas.witkowski at tu-dresden.de> wrote:
> I want to solve some (weakly) coupled system of equations of the following > form: > > A B u > . = ..... > 0 C v > > > so, C is the discrete Laplacian and A and B are some more complicated > operators (I make use of linear finite elements). All boundary conditions > are periodic, so the unknown v is determined only up to a constant. A and B > contain both the identity operator, so u is fixed. Now I want to solve the > system on the whole (there are reasons to do it in this way!) and I must > provide information about the nullspace to the solver. When I am right, to > provide the correct nullspace I must solve one equation with A. Is there > any way in PETSc to circumvent the problem? If I understand you correctly, your null space vector is (0 I). I use the same null space for SNES ex62. Note that you should probably use FieldSplit multiplicative here since you have a block triangular system to start with. Matt > > Thomas -- 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/20120817/a1c5c254/attachment.html>
