[petsc-users] MatMatSolve in sequential call

[Matthew Knepley]

On Tue, Aug 21, 2012 at 11:25 AM, Alexander Grayver <agrayver at gfz-potsdam.de
> wrote:

>  On 21.08.2012 18:14, Hong Zhang wrote:
>
> Alexander :
>
> Testing your matrix A.dat
> using petsc-3.3/src/ksp/ksp/examples/tutorials/ex10.c,
> I find that A is numerically singular:
>
>
> Hong,
>
> Sorry, but I forgot to mention that this is double complex symmetric
> matrix. Did you load and treat it like that?
>
>  I'm convinced that matrix A is corrupted or obtained from an incorrect
> numerical model.
> Also note, your matrix A has size of approx. 60k, which is too large for
> sequential direct solver.
>
>
> MUMPS takes only several minutes and 6 GB of memory to factorize it.
> This factorization gives residual on the order of 10e-12 and solution is
> indeed correct.
>
> Nevertheless, you're right, there is numerical null-space in this matrix
> since it comes
> from the discretization of equation that contains curl curl operator, but
> practically this
> case is not really the worst one.
>

This makes no sense whatsoever. How can you LU factor a matrix that has a
null space?

   Matt


>
>  The error on MatMatSolve() when calling
> ' -pc_type cholesky -pc_factor_mat_solver_package mumps'
> is a bug in our petsc-mumps interface. I've pushed a fix to petsc-3.3
> http://petsc.cs.iit.edu/petsc/releases/petsc-3.3/rev/8badc49a596e
>
>  Thanks for your report.
>
>
> Thank you for the patch.
>
> --
> Regards,
> Alexander
>
>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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