[petsc-users] GAMG failure

[Mark Adams]

On Tue, Mar 28, 2023 at 12:38 PM Blaise Bourdin <bourdin at mcmaster.ca> wrote:

>
>
> On Mar 27, 2023, at 9:11 PM, Mark Adams <mfadams at lbl.gov> wrote:
>
> Yes, the eigen estimates are converging slowly.
>
> BTW, have you tried hypre? It is a good solver (lots lots more woman years)
> These eigen estimates are conceptually simple, but they can lead to
> problems like this (hypre and an eigen estimate free smoother).
>
> I just moved from petsc 3.3 to main, so my experience with an old version
> of hyper has not been very convincing. Strangely enough, ML has always been
> the most efficient PC for me.
>

ML is a good solver.


> Maybe it’s time to revisit.
> That said, I would really like to get decent performances out of gamg. One
> day, I’d like to be able to account for the special structure of
> phase-field fracture in the construction of the coarse space.
>
>
> But try this (good to have options anyway):
>
> -pc_gamg_esteig_ksp_max_it 20
>
> Chevy will scale the estimate that we give by, I think, 5% by default.
> Maybe 10.
> You can set that with:
>
> -mg_levels_ksp_chebyshev_esteig 0,0.2,0,*1.05*
>
> 0.2 is the scaling of the high eigen estimate for the low eigen value in
> Chebyshev.
>
>
>
> Jed’s suggestion of using -pc_gamg_reuse_interpolation 0 worked.
>

OK, have to admit I am surprised.
But I guess with your fracture the matrix/physics/dynamics does change a lot


> I am testing your options at the moment.
>

There are a lot of options and it is cumbersome but they are finite and
good to know.
Glad its working,


>
> Thanks a lot,
>
> Blaise
>
> —
> Canada Research Chair in Mathematical and Computational Aspects of Solid
> Mechanics (Tier 1)
> Professor, Department of Mathematics & Statistics
> Hamilton Hall room 409A, McMaster University
> 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada
> https://www.math.mcmaster.ca/bourdin | +1 (905) 525 9140 ext. 27243
>
>
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