[petsc-users] Laplace Equation preconditioner

[Barry Smith]

   What KSP are you using? DIVERGED_BREAKDOWN is very rare for KSPGMRES. If you are using one of its lesser cousins like bcgs you might consider switching to bcgsl or gmres.

   I assume because of boundary conditions or the discretization you do not have symmetric positive definite and thus cannot use CG.

  Barry


> On Oct 12, 2022, at 2:00 PM, Matthew Knepley <knepley at gmail.com> wrote:
> 
> On Wed, Oct 12, 2022 at 1:38 PM Alfredo J Duarte Gomez <aduarteg at utexas.edu <mailto:aduarteg at utexas.edu>> wrote:
> Good morning PETSC users,
> 
> I have a current solver that requires the solution of a Laplace equation to be reused for all future time steps.
> 
> The configuration is axisymmetric with Dirichlet BCs at the top and bottom boundaries, and Zero Neumman conditions at the axis and far field. The grid is curvilinear and structured. 
> 
> So far I have been using PCHYPRE boomeramg as the preconditioner, which often works well, but I have also experienced DIVERGED_BREAKDOWN on many occasions. When I use direct solver PCMUMPS it always produces a satisfactory answer, which gives me confidence that the solution exists for the given grid in all these configurations where boomeramg fails.
> 
> I do not know why Hypre is breaking down. Did you try ML or GAMG? They are easier to diagnose I think.
> 
>   Thanks,
> 
>      Matt
>  
> I am looking for recommendations on other preconditioners to try in this problem that can produce a solution faster than PCMUMPS, or recommendations on which parameters to adjust on boomeramg.
> 
> Thank you,
> 
> 
> -- 
> Alfredo Duarte
> Graduate Research Assistant
> The University of Texas at Austin
> 
> 
> -- 
> What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.
> -- Norbert Wiener
> 
> https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>

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