[petsc-users] MatSetNearNullSpace and BoomerAMG ?

[Natacha BEREUX]

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).

Does it make sense ?
Is this setting only relevant for Smoothed Aggregation AMG ? and of no use
for BoomeAMG? Or do I miss something in the setting ?
Thanks a lot,
Best regards
Natacha
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