On Fri, Aug 17, 2012 at 2:06 PM, Thomas Witkowski < thomas.witkowski at tu-dresden.de> wrote:
> Am 17.08.2012 16:24, schrieb Matthew Knepley: > > 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. > > (0 I) cannot be an element of the null space, as multiplying it with the > matrix results in a non-zero vector. Or am I totally wrong about null > spaces of matrices? > Maybe you could as your question again. I am not understanding what you want. 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/c23563c1/attachment.html>
