[petsc-users] Elliptic operator with Neumann conditions

[Matthew Knepley]

On Thu, Feb 8, 2018 at 4:43 AM, Marco Cisternino <
marco.cisternino at optimad.it> wrote:

> Hi everybody,
> I would like to ask what solution is computed if I try to solve the linear
> system relative to the problem in subject without creating the null space.
> I tried with and without the call to
> MatNullSpaceCreate(m_communicator, PETSC_TRUE, 0, NULL, &nullspace);
> and I get zero averaged solution with and the same solution plus a
> constant without.
> How does PETSc  work in the second case?
>

It depends on the Krylov method you use and the initial residual. We do not
do anything special.

  Thanks,

     Matt


> Does it check the matrix singularity? And is it able to create the null
> space with the constant automatically?
> Thanks.
>
>
> Marco Cisternino, PhD
> marco.cisternino at optimad.it
> _______________________________
> OPTIMAD Engineering srl
> Via Giacinto Collegno 18, Torino, Italia.
> +3901119719782
> www.optimad.it
>
>


-- 
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

https://www.cse.buffalo.edu/~knepley/ <http://www.caam.rice.edu/~mk51/>
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