[petsc-users] MatSetNearNullSpace and BoomerAMG ?

[Natacha BEREUX]

OK, thanks a lot Jed for your quick answer.

I have a second question on multigrid :
I define a matrix block size (equal to 3). Is this mandatory for any type
of multigrid preconditioner (BoomerAMG, ML and GAMG) ?
Or is it only  required with  ML and GAMG ?

Best regards
Natacha




On Fri, Jul 18, 2014 at 3:07 PM, Jed Brown <jed at jedbrown.org> wrote:

> Natacha BEREUX <natacha.bereux at gmail.com> writes:
>
> > Dear all,
> >
> > I am testing three multigrid preconditionners: BoomerAMG, ML and GAMG on
> a
> > 3D elasticity problem (a cube with prescribed displacement on upper and
> > lower faces).
> > I set the null space by calling  MatNullSpaceCreateRigidBody and then
> > MatSetNearNullSpace).
> >
> > I see a difference (about half iterations) for ML and GAMG but nothing
> > happens with BoomerAMG (same number of iterations with and without
> setting
> > the NearNullspace).
>
> That's expected because BoomerAMG does not use any such information
> (though the algorithm might be extended in the future so that those
> vectors become seed vectors for Bootstrap AMG, for example; I don't know
> if the BoomerAMG developers have any interest in implementing this).
>
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