On Sun, 12 Aug 2007, Zhu Liang wrote:
> Yes, you are right, I am trying to solve Oseen equation. > > I tried using preconditioner PCILU(1) which works well. > But for PCILU(0) it did not work, as well as PCBJACOBI. > I have tried to insert zero on the diagonal, but it still does not work. > > In your opinion, what is the best parallel solver and preconditioner > for the Oseen equation ? Black box? I wish I did! Matt, when are we going to add a "general purpose" Stokes solver to PETSc? Does that question even make sense? Barry > > Thanks for your reply. > Liang > > On 8/12/07, Barry Smith <bsmith at mcs.anl.gov> wrote: > > > > > > It is not really the BiCGstab Krylov solver that it complaining; > > it is the default ILU or block Jacobi with ILU on the blocks that is > > complaining. > > > > You first need to make sure you insert 0 entries on the all the diagonal > > entries that are 0. BUT given the structure of your matrix you may want > > to think about solvers that specifically handle that type of matrix. > > > > Barry > > > > Stokes type solvers? > > > > > > On Mon, 13 Aug 2007, Zhu Liang wrote: > > > > > By the way, the block of my matrix is like : > > > > > > U , a > > > A^T , 0 > > > > > > > > > > > > ---------- Forwarded message ---------- > > > From: Zhu Liang <liangcanada at gmail.com> > > > Date: Aug 13, 2007 5:46 AM > > > Subject: How can I use BICGStab on a matrix with zero entries on the > > > diagonal > > > To: petsc-users at mcs.anl.gov > > > > > > > > > Dear petsc-users > > > > > > When I try to solve a linear equation Ax=b with BicgStab preconditioner, > > I > > > got > > > an error "Matrix is missing diagonal number". That is because I have > > zeros > > > on > > > the diagonal of the matrix. > > > > > > I am wondering if there is some simple method to avoid that? > > > > > > Best, > > > Liang > > > > > > > >
