[petsc-users] Solver/Preconditioner suggestions

[Alfredo J Duarte Gomez]

Hello Matthew,

Thank you for your suggestion on the Laplace solver.

About the other systems I would say B and C are mostly dominated by
advection, except for diffusive layers at the boundaries.

A is a bit more difficult to judge, although it can be expected to have a
very large advective component, it also has a large reactive component, and
the diffusion dominated layers at the boundaries.

Thank you,

-Alfredo

On Thu, May 19, 2022 at 12:31 PM Matthew Knepley <knepley at gmail.com> wrote:

> On Thu, May 19, 2022 at 7:27 AM Alfredo J Duarte Gomez <
> aduarteg at utexas.edu> wrote:
>
>> Good afternoon PETSC users,
>>
>> I am looking for some suggestions on preconditioners/solvers.
>>
>> Currently, I have a custom preconditioner that solves 4 independent
>> systems, let's call them A,B,C, and D.
>>
>> A is an advective, diffusive, reactive system, although due to some
>> coefficient it is the system with the highest condition number and
>> therefore the most difficult to solve.
>>
>> B and C, are more "standard" advective, diffusion, reactive systems. The
>> condition number is not as high as A.
>>
>> D is simply the laplacian used to solve an elliptic Poisson equation.
>>
>> For more context, A,B, and C need to be recomputed about once every time
>> step, while D is a one time cost.
>>
>> The problem is 2-D, sizes are on the order of 1-10 million grid points,
>> and I am using a structured grid. These usually run on somewhere between
>> 100-400 processors.
>>
>> Currently  I am solving A,B, and C with the HYPRE Euclid algorithm
>> ILU(1), and D is solved with the direct solver MUMPS.
>>
>> While these were very useful to get the code working, I am now trying to
>> get better parallel scaling/efficiencies and performance. HYPRE euclid does
>> not seem to scale super well beyond like 60 procs, and MUMPS has very large
>> memory requirements.
>>
>> Does anyone have suggestions on more scalable ILU algorithms for A,B, and
>> C, or any other good alternatives?
>>
>
> Are these advectively dominated?
>
>
>> From what I have read, multigrid methods are probably the best
>> alternative for D, but I have very little experience with these and they
>> seem to require a lot of parameters. Does anyone have pointers on a good
>> setup for a multigrid preconditioner?
>>
>
> This is the easy one. If you are using DMDA, just turn on -pc_type mg and
> give a number of levels and it should be fine. If not, then use GAMG and it
> should be fine, You could also use Hypre Boomeramg for this since it is
> optimized for the 2D Laplacian.
>
>   Thanks,
>
>     Matt
>
>
>> Thank you and have a good day,
>>
>> -Alfredo
>>
>> --
>> 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/>
>


-- 
Alfredo Duarte
Graduate Research Assistant
The University of Texas at Austin
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