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

["Zhu Liang" <liangcanada@xxxxxxxxx>]

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 ?

Thanks for your reply.
Liang

On 8/12/07, Barry Smith <bsmith@xxxxxxxxxxx> 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@xxxxxxxxx>
> 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@xxxxxxxxxxx
>
>
> 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
>