[petsc-users] compiler preprocessor for PETSc

[Michael Wick]

Hi PETSc team:

What is an appropriate compiler preprocessor to tell the code PETSc has
been initialized?

Mike

[petsc-users] Monolithic AMG with fieldsplit as smoother

[Michael Wick]

Hello PETSc team:

I wonder if the current PETSc implementation supports using AMG
monolithically for a multi-field problem and using fieldsplit in the
smoother.

Thank you very much,

Mike

[petsc-users] pass a member function to MatShellSetOperation

[Michael Wick]

Hi:

I want to have the shell matrix-vector multiplication written as a class
member function and pass it to the shell matrix via MatShellSetOperation.

MatShellSetOperation(A, MATOP_MULT, (void
(*)(void))(_Assem::MyMatMult));

Perhaps I have a wrong understanding of function pointers, and I am
constantly getting warnings that say I cannot convert a member function to
a void type. The warning indeed makes sense to me, as the function pointer
passed in the above manner is independent of an instance. Perhaps there are
other ways of passing a member function that I don't know of. If you know
how to address this, I would appreciate it a lot!

Thanks,

Mike

Re: [petsc-users] Failure of MUMPS

[Michael Wick]

Thanks for all the suggestions!

Increasing the value of icntl_14 in MUMPS helps a lot for my case.

Do you have any suggestions for higher-order methods in saddle-point
problems?

Mike

Dave May  于2018年10月11日周四 上午1:50写道：

>
>
> On Sat, 6 Oct 2018 at 12:42, Matthew Knepley  wrote:
>
>> On Fri, Oct 5, 2018 at 9:08 PM Mike Wick 
>> wrote:
>>
>>> Hello PETSc team:
>>>
>>> I am trying to solve a PDE problem with high-order finite elements. The
>>> matrix is getting denser and my experience is that MUMPS just outperforms
>>> iterative solvers.
>>>
>>
>> If the problem is elliptic, there is a lot of evidence that the P1
>> preconditioner is descent for the system. Some people
>> just project the system to P1, invert that with multigrid, and use that
>> as the PC for Krylov. It should be worth trying.
>>
>
> Matt means project to P1 directly from your high order function space in
> one step. It is definitely worth trying.
> For those interested, this approach is first described and discussed (to
> my knowledge) in this paper:
>
> Persson, Per-Olof, and Jaime Peraire. "An efficient low memory implicit DG
> algorithm for time dependent problems." *44th AIAA Aerospace Sciences
> Meeting and Exhibit*. 2006.
>
>
>> Moreover, as Jed will tell you, forming matrices for higher order is
>> counterproductive. You should apply those matrix-free.
>>
>
> I definitely agree with that.
>
> Cheers,
>   Dave
>
>
>
>>
>>   Thanks,
>>
>>  Matt
>>
>>
>>> For certain problems, MUMPS just fail in the middle for no clear reason.
>>> I just wander if there is any suggestion to improve the robustness of
>>> MUMPS? Or in general, any suggestion for interative solver with very
>>> high-order finite elements?
>>>
>>> Thanks!
>>>
>>> Mike
>>>
>>
>>
>> --
>> 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/
>> 
>>
>