How can I use BICGStab on a matrix with zero entries on the diagonal

[Barry Smith]

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
> > >
> >
> >
>