[petsc-users] About Preconditioner and MUMPS

[Matthew Knepley]

On Tue, Dec 6, 2022 at 5:16 AM 김성익 <ksi2443 at gmail.com> wrote:

> Hello,
>
>
>
> I have some questions about pc and mumps_icntl.
>
> 1.     What’s the difference between adopt preconditioner by code (for
> example, PetscCall(PCSetType(pc,PCLU)) and option -pc_type lu??
>
If you call KSPSetFromOptions(), then they are the same.


> And also, What’s the priority between code pcsettype and option -pc_type ??
>
 PCSetType() will force the change. If you call KSPSetFromOptions() after
that, -pc_type will override the change.

2.     When I tried to use METIS in MUMPS, I adopted metis by option (for
> example, -mat_mumps_icntl_7 5). In this situation, it is impossible to use
> metis without pc_type lu.
>
This is incorrect. You might still call PCSetType() if you want, but you
must call KSPSetFromOptions() after that.


> However, in my case pc type lu makes the performance poor. So I don’t want
> to use lu preconditioner. How can I do this?
>
This statement is incoherent. MUMPS is LU preconditioning, so if you use
MUMPS you are using LU.

  Thanks,

     Matt


> Thanks,
>
> Hyung Kim
>


-- 
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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