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

[Barry Smith]

  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
>