[petsc-users] Using nonzero -pc_hypre_boomeramg_restriction_type in field split

[Pierre Jolivet]

> On 14 Apr 2023, at 7:02 AM, Alexander Lindsay <alexlindsay239 at gmail.com> wrote:
> 
> Pierre,
> 
> This is very helpful information. Thank you. Yes I would appreciate those command line options if you’re willing to share!

No problem, I’ll get in touch with you in private first, because it may require some extra work (need a couple of extra options in PETSc ./configure), and this is not very related to the problem at hand, so best not to spam the mailing list.

Thanks,
Pierre

>> On Apr 13, 2023, at 9:54 PM, Pierre Jolivet <pierre.jolivet at lip6.fr> wrote:
>> 
>> 
>> 
>>> On 13 Apr 2023, at 10:33 PM, Alexander Lindsay <alexlindsay239 at gmail.com> wrote:
>>> 
>>> Hi, I'm trying to solve steady Navier-Stokes for different Reynolds numbers. My options table
>>> 
>>> -dm_moose_fieldsplit_names u,p
>>> -dm_moose_nfieldsplits 2
>>> -fieldsplit_p_dm_moose_vars pressure
>>> -fieldsplit_p_ksp_type preonly
>>> -fieldsplit_p_pc_type jacobi
>>> -fieldsplit_u_dm_moose_vars vel_x,vel_y
>>> -fieldsplit_u_ksp_type preonly
>>> -fieldsplit_u_pc_hypre_type boomeramg
>>> -fieldsplit_u_pc_type hypre
>>> -pc_fieldsplit_schur_fact_type full
>>> -pc_fieldsplit_schur_precondition selfp
>>> -pc_fieldsplit_type schur
>>> -pc_type fieldsplit
>>> 
>>> works wonderfully for a low Reynolds number of 2.2. The solver performance crushes LU as I scale up the problem. However, not surprisingly this options table struggles when I bump the Reynolds number to 220. I've read that use of AIR (approximate ideal restriction) can improve performance for advection dominated problems. I've tried setting -pc_hypre_boomeramg_restriction_type 1 for a simple diffusion problem and the option works fine. However, when applying it to my field-split preconditioned Navier-Stokes system, I get immediate non-convergence:
>>> 
>>>  0 Nonlinear |R| = 1.033077e+03
>>>       0 Linear |R| = 1.033077e+03
>>>   Linear solve did not converge due to DIVERGED_NANORINF iterations 0
>>> Nonlinear solve did not converge due to DIVERGED_LINEAR_SOLVE iterations 0
>>> 
>>> Does anyone have an idea as to why this might be happening?
>> 
>> Do not use this option, even when not part of PCFIELDSPLIT.
>> There is some missing plumbing in PETSc which makes it unusable, see Ben’s comment here https://github.com/hypre-space/hypre/issues/764#issuecomment-1353452417.
>> In fact, it’s quite easy to make HYPRE generate NaN with a very simple stabilized convection—diffusion problem near the pure convection limit (something that ℓAIR is supposed to handle).
>> Even worse, you can make HYPRE fill your terminal with printf-style debugging messages https://github.com/hypre-space/hypre/blob/5546cc22d46b3dba253849f258786da47c9a7b21/src/parcsr_ls/par_lr_restr.c#L1416 with this option turned on.
>> As a result, I have been unable to reproduce any of the ℓAIR results.
>> This also explains why I have been using plain BoomerAMG instead of ℓAIR for the comparison in page 9 of https://arxiv.org/pdf/2201.02250.pdf (if you would like to try the PC we are using, I could send you the command line options).
>> 
>> Thanks,
>> Pierre
>> 
>>> If not, I'd take a suggestion on where to set a breakpoint to start my own investigation. Alternatively, I welcome other preconditioning suggestions for an advection dominated problem.
>>> 
>>> Alex
>> 

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