[petsc-users] Configure nested PCFIELDSPLIT with general index sets

[Natacha BEREUX]

Dear Matt,
Sorry for my (very) late reply.
I was not able to find the Fortran interface of
DMSellSetCreateFieldDecomposition in the late petsc-3.7.6 fortran (and my
code still fails to link).
I have the feeling that it is missing in the master branch.
And I was not able to get it on bitbucket either.
Is there a branch from which I can pull your commit  ?
Thans a lot for your help,
Natacha

On Thu, Mar 30, 2017 at 9:25 PM, Matthew Knepley <knepley at gmail.com> wrote:

> On Wed, Mar 22, 2017 at 1:45 PM, Natacha BEREUX <natacha.bereux at gmail.com>
> wrote:
>
>> Hello Matt,
>> Thanks a lot for your answers.
>> Since I am working on a large FEM Fortran code, I have to stick to
>> Fortran.
>> Do you know if  someone plans to add this Fortran interface? Or may be I
>> could do it myself ? Is this particular interface very hard to add ?
>> Perhaps could  I mimic some other interface ?
>> What would you advise ?
>>
>
> I have added the interface in branch knepley/feature-fortran-compose. I
> also put this in the 'next' branch. It
> should make it to master soon. There is a test in sys/examples/tests/ex13f
>
>   Thanks,
>
>     Matt
>
>
>> Best regards,
>> Natacha
>>
>> On Wed, Mar 22, 2017 at 12:33 PM, Matthew Knepley <knepley at gmail.com>
>> wrote:
>>
>>> On Wed, Mar 22, 2017 at 10:03 AM, Natacha BEREUX <
>>> natacha.bereux at gmail.com> wrote:
>>>
>>>> Hello,
>>>> if my understanding is correct, the approach proposed by Matt and
>>>> Lawrence is the following :
>>>> - create a DMShell (DMShellCreate)
>>>> - define my own CreateFieldDecomposition to return the index sets I
>>>> need (for displacement, pressure and temperature degrees of freedom) :
>>>> myCreateFieldDecomposition(... )
>>>> - set it in the DMShell ( DMShellSetCreateFieldDecomposition)
>>>> - then sets  the DM in KSP context  (KSPSetDM)
>>>>
>>>> I  have some more questions
>>>> - I did not succeed in setting my own CreateFieldDecomposition in the
>>>> DMShell : link  fails with " unknown reference to «
>>>> dmshellsetcreatefielddecomposition_ ». Could it be a Fortran problem
>>>> (I am using Fortran)?  Is this routine available in PETSc  Fortran
>>>> interface ? \
>>>>
>>>
>>> Yes, exactly. The Fortran interface for passing function pointers is
>>> complex, and no one has added this function yet.
>>>
>>>
>>>> - CreateFieldDecomposition is supposed to return an array of dms (to
>>>> define the fields). I am not able to return such datas.  Do I return a
>>>> PETSC_NULL_OBJECT instead ?
>>>>
>>>
>>> Yes.
>>>
>>>
>>>> - do I have to provide something else to define the DMShell ?
>>>>
>>>
>>> I think you will have to return local and global vectors, but this just
>>> means creating a vector of the correct size and distribution.
>>>
>>>   Thanks,
>>>
>>>      Matt
>>>
>>>
>>>> Thanks a lot for your help
>>>> Natacha
>>>>
>>>> On Tue, Mar 21, 2017 at 2:44 PM, Natacha BEREUX <
>>>> natacha.bereux at gmail.com> wrote:
>>>>
>>>>> Thanks for your quick answers. To be honest, I am not familiar at all
>>>>> with DMShells and DMPlexes. But since it is what I need, I am going to try
>>>>> it.
>>>>> Thanks again  for your advices,
>>>>> Natacha
>>>>>
>>>>> On Tue, Mar 21, 2017 at 2:27 PM, Lawrence Mitchell <
>>>>> lawrence.mitchell at imperial.ac.uk> wrote:
>>>>>
>>>>>>
>>>>>> > On 21 Mar 2017, at 13:24, Matthew Knepley <knepley at gmail.com>
>>>>>> wrote:
>>>>>> >
>>>>>> > I think the remedy is as easy as specifying a DMShell that has a
>>>>>> PetscSection (DMSetDefaultSection) with your ordering, and
>>>>>> > I think this is how Firedrake (http://www.firedrakeproject.org/)
>>>>>> does it.
>>>>>>
>>>>>> We actually don't use a section, but we do provide
>>>>>> DMCreateFieldDecomposition_Shell.
>>>>>>
>>>>>> If you have a section that describes all the fields, then I think if
>>>>>> the DMShell knows about it, you effectively get the same behaviour as
>>>>>> DMPlex (which does the decomposition in the same manner?).
>>>>>>
>>>>>> > However, I usually use a DMPlex which knows about my
>>>>>> > mesh, so I am not sure if this strategy has any holes.
>>>>>>
>>>>>> I haven't noticed anything yet.
>>>>>>
>>>>>> Lawrence
>>>>>
>>>>>
>>>>>
>>>>
>>>
>>>
>>> --
>>> 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
>>>
>>
>>
>
>
> --
> 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
>
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