[petsc-users] GAMG failure

Jed Brown jed at jedbrown.org
Tue Mar 28 12:18:50 CDT 2023

This suite has been good for my solid mechanics solvers. (It's written here as a coarse grid solver because we do matrix-free p-MG first, but you can use it directly.)


Blaise Bourdin <bourdin at mcmaster.ca> writes:

>  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. 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. I am testing your options at the moment.
> 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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