[petsc-users] Inquiry about the interpolation and restriction matrix for PCMG

[Xiaodong Liu]

The issue is that, I tested non-Galerkin type without setting up coarse
operators explicitly using  PCMGSetOperators, but it worked pretty well.
Thanks,
Xiaodong Liu, PhD
X: Computational Physics Division
Los Alamos National Laboratory
P.O. Box 1663,
Los Alamos, NM 87544
505-709-0534


On Fri, Mar 20, 2020 at 8:28 PM Xiaodong Liu <xliu29 at ncsu.edu> wrote:

> Thanks a lot, Matthew and Mark !
> Take care.
> Xiaodong Liu, PhD
> X: Computational Physics Division
> Los Alamos National Laboratory
> P.O. Box 1663,
> Los Alamos, NM 87544
> 505-709-0534
>
>
> On Fri, Mar 20, 2020 at 6:50 PM Matthew Knepley <knepley at gmail.com> wrote:
>
>> On Fri, Mar 20, 2020 at 6:26 PM Xiaodong Liu <xliu29 at ncsu.edu> wrote:
>>
>>> Hi, Petsc team,
>>>
>>> I am practising  PCMG using the following case (3DQ1)
>>>
>>> https://www.mcs.anl.gov/petsc/petsc-current/src/ksp/ksp/examples/tutorials/ex45.c.html
>>>
>>>
>>> I have several questions.
>>> *1)  About the interpolation and restriction matrix*
>>>
>>> For both Galerkin and non-Galerkin type, the interpolation matrix P  is
>>> based on the trilinear interpolation (*I found the source code*) and
>>> the restriction one R is 1/8*P^T?
>>> *Could you please tell me where  the source code to define the
>>> restriction matrix is? *
>>> *2) About the operator on the coarse level*
>>>
>>>  It is straightforward to calculate the operator on the coarse level
>>> for Galerkin type by R*A*P. But how did you define the operator for
>>> non-Galerkin type?
>>>
>>
>> non-Galerkin usually means rediscretization, where the user explicitly
>> supplies the coarser operations, using
>>
>>
>> https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/PC/PCMGSetOperators.html
>>
>>    Thanks,
>>
>>       Matt
>>
>>
>>> Did you use DMRestrict ? Could you please tell me where is the source
>>> code to define
>>> (*link->restricthook)(fine,restrct,rscale,inject,coarse,link->ctx);
>>> in
>>> 2933: PetscErrorCode DMRestrict(DM fine,Mat restrct,Vec rscale,Mat
>>> inject,DM coarse)
>>> 2934: {
>>> 2935:   PetscErrorCode    ierr;
>>> 2936:   DMCoarsenHookLink link;
>>>
>>> 2939:   for (link=fine->coarsenhook; link; link=link->next) {
>>> 2940:     if (link->restricthook) {
>>> 2941:
>>> (*link->restricthook)(fine,restrct,rscale,inject,coarse,link->ctx);
>>> 2942:     }
>>> 2943:   }
>>> 2944:   return(0);
>>> 2945: }
>>> on
>>>
>>> https://www.mcs.anl.gov/petsc/petsc-current/src/dm/interface/dm.c.html#DMRestrict
>>>
>>>
>>> Thanks a lot !
>>> Take care!
>>> Xiaodong
>>>
>>>
>>>
>>> Xiaodong Liu, PhD
>>> X: Computational Physics Division
>>> Los Alamos National Laboratory
>>> P.O. Box 1663,
>>> Los Alamos, NM 87544
>>> 505-709-0534
>>>
>>
>>
>> --
>> 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/>
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20200321/6e674736/attachment.html>