[petsc-users] MatSetNearNullSpace and BoomerAMG ?

[Jed Brown]

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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