[petsc-users] Definition of threshold(s) in gamg and boomerAMG

[Mark Adams]

These thresholds are for completely different coursening algorithms.
GAMG just drops edges below the threshold and hypre (classical AMG) does
something completely different.

Mark

On Fri, Jan 6, 2023 at 10:43 AM Edoardo Centofanti <
edoardo.centofanti01 at universitadipavia.it> wrote:

> Hi PETSc users,
>
> I was looking for the exact definitions of the threshold parameter
> (-pc_gamg_threshold) for gamg and of the strong threshold
> (-pc_hypre_boomeramg_strong_threshold) for Hypre BoomerAMG. My curiosity
> comes from the fact that the suggested parameters (apparently acting on the
> same aspect of the algorithms) differ of around one order of magnitude (if
> I remember right from the PETSc manual, the gamg threshold for 3D problems
> is around 0.05, while for boomerAMG ranges from 0.25 to 0.5).
>
> Thank you in advance,
> Edoardo
>
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