Solve a symmetric matrix

Hong Zhang hzhang at
Tue Oct 2 08:51:47 CDT 2007

PCILU and PCICC are not supported for MPISBAIJ matrix type
(the error message should indicate this problem).
For sequential sbaij matrix, you can use PCICC.
For parallel, you may try the default petsc preconditioner
block jacobi + icc. See Chapter 4 of petsc user manual.

You can start testing a petsc example
~petsc/src/ksp/ksp/examples/tutorials/ex5.c with runtime options:
mpirun -np 2 ex5 -mat_type sbaij -mat_ignore_lower_triangular -ksp_view

On Tue, 2 Oct 2007, LECAS Dimitri wrote:

> Hi,
> I try to solve a symmetric problem, i use MatCreateMPISBAIJ for the
> matrix  but i have an error message about the preconditioning (PCILU).
> With the option -pc_type none, i have big problem with convergence
> (residual > 1e32). So my question is what the option (for ksp and pc) to
> use for symmetric problem.
> I not sure i understand the meaning of block size in MatCreateMPISBAIJ,
> i set it to 1.

When set the block size=1, you acturally use a symmetric matrix
that only stores upper triangular part.


> Best Regards.
> --
> Dimitri Lecas

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