[petsc-users] mumps solve with same nonzero pattern

[Matthew Knepley]

On Fri, Apr 27, 2012 at 9:53 AM, Wen Jiang <jiangwen84 at gmail.com> wrote:

> Hi,
>
> I am using mumps in PETSc to solve a 0.2 million system on 128 cores.
> Within Newton-Raphson iteration, the system with same sparse structure but
> different values will be solved many times. And I specify the
> preconditioning matrix having same nonzero pattern. The first time solving
> costs around 900 seconds and later solving only takes around 200 seconds.
> So I am wondering why the time differs that much. By setting the same
> nonzero pattern of pc, which of the mumps control parameters does PETSc
> change? Thanks.
>

The difference is that you do not have to perform the symbolic
factorization again if the nonzero pattern does not change,
just the numeric factorization. The symbolic factorization is the costly
step.

   Matt


> Regards,
> Wen
>



-- 
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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