On Tue, Sep 13, 2011 at 5:56 AM, Marco Cisternino < marco.cisternino at polito.it> wrote:
> Hi to everybody, > I'm trying to solve this equation > nabla(k*nabla(u))=f, > with neumann homogeneous boundary conditions, where k is piecewise > constant and f is a zero mean source (compatibility is respected). > To do this I solve an extended by transmission conditions linear system, > obtained with FD second order scheme. > Everything works fine with dirichlet bc and with neumann bc too, if the > interface, where k jumps, cut the computational domain. > But if the interface is in the middle of the computational domain, > something wrong happens where the processes overlap, with an overall loss of > symmetry: the source, the interface and the bc are symmetric. > I use gmres with asm. These are the lines to create the nullspace > > has_cnst=PETSC_TRUE > call MatNullSpaceCreate(MPI_CART_**COMM,has_cnst,0,PETSC_NULL_** > OBJECT,nsppoi,ierr) > call KSPSetNullSpace(ksppoi,nsppoi,**ierr) > > Ask me everything you need to better understand the problem. > Could you help me? > If you have matrices, or submatrices, which must be symmetric, you can check this using http://www.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/Mat/MatIsSymmetric.html Thanks, Matt > Thanks. > > Marco > > -- > Marco Cisternino > PhD Student > Politecnico di Torino > Email:marco.cisternino at polito.**it <Email%3Amarco.cisternino at polito.it> > > -- 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/20110913/8054b03f/attachment.htm>
