[petsc-users] GAMG failure

Jed Brown jed at jedbrown.org
Fri Mar 24 13:47:02 CDT 2023

You can -pc_gamg_threshold .02 to slow the coarsening and either stronger smoother or increase number of iterations used for estimation (or increase tolerance). I assume your system is SPD and you've set the near-null space.

Blaise Bourdin <bourdin at mcmaster.ca> writes:

> Hi,
> I am having issue with GAMG for some very ill-conditioned 2D linearized elasticity problems (sharp variation of elastic moduli with thin  regions of nearly incompressible material). I use snes_type newtonls, linesearch_type cp, and pc_type gamg without any further options. pc_type Jacobi converges fine (although slowly of course).
> I am not really surprised that gamg would not converge out of the box, but don’t know where to start to investigate the convergence failure. Can anybody help?
> 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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