[petsc-users] Distributing data along with DMPlex

[Matthew Knepley]

On Thu, Dec 17, 2015 at 1:27 PM, Justin Chang <jychang48 at gmail.com> wrote:

> So you would use something like DMPlexDistributeField()
> <http://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/DM/DMPlexDistributeField.html> in
> that case. You have your original/global DM, PetscSection, and Vec of
> values. Then using the PetscSF that was created during DMPlexDistribute,
> you map the global stuff into the local stuff.
>

Justin is correct. However, I will note that this strategy is not scalable.
Usually the data is much larger than the mesh,
so this runs out of memory much sooner. Are you sure that this is what you
want?

  Thanks,

     Matt


> On Thu, Dec 17, 2015 at 11:21 AM, Alejandro D Otero <aotero at fi.uba.ar>
> wrote:
>
>> Thanks,
>> The problem then is that after DMPlexDistribute the DMPlex 'points' are
>> renumbered. So if the values are related to each point in the original
>> numbering how do I set the values after the distribution. I know the
>> property stored in the vector related to the entities with the numbering of
>> the original mesh which I use to create the first DMPlex.
>>
>> Ideally for me, I would like to set the values in the vector before
>> DMPlexDistribute and get the vector components renumbered and redistributed
>> accordingly in a global vector. And then, get the local vector.
>>
>> Hope it could be more clear now.
>> Regards,
>>
>> Alejandro
>>
>>
>>
>> On Wed, Dec 16, 2015 at 7:01 PM, Justin Chang <jychang48 at gmail.com>
>> wrote:
>>
>>> I think you would follow this order:
>>>
>>> 1*) create a DMPlex (depth, chart, etc) on rank 0. Other ranks have an
>>> empty DM
>>>
>>> 2) DMPlexDistribute()
>>>
>>> 3*) Create the PetscSection
>>>
>>> 4) DMCreateGlobalVector()
>>>
>>> 5) DMCreateLocalVector()
>>>
>>> Now you have a global vector and a local vector for your distributed
>>> DMPlex. The mapping/ghosting/etc of dofs is already taken care of.
>>>
>>> * if you're using standard Galerkin FE then in SNES examples 12 and 62
>>> (and maybe others?) the first step is handled through the mesh generation
>>> functions and step 3 is handled through step 4
>>>
>>> Thanks,
>>> Justin
>>>
>>> On Wednesday, December 16, 2015, Alejandro D Otero <aotero at fi.uba.ar>
>>> wrote:
>>>
>>>> Hi, I need some help understanding how to distribute data together with
>>>> a dmplex representing a FE mesh.
>>>> At the beginning I define the structure of the dmplex assigning certain
>>>> number of DoF to cells, edges and vertexes, in one process (the dmplex in
>>>> the rest is empty)
>>>> I create a petscsecton and I create an associated global vector with
>>>> the quantities I want to store.
>>>> Then I distribute the dmplex over all the processes.
>>>> * Although this does not perform well it is just a starting point. I
>>>> know it has to be improved.
>>>>
>>>> I would like to have the global vector distributed accordingly so that
>>>> each process has access to the corresponding local part with its DoF
>>>> (possibly adding some ghost values corresponding to the shared DoF not
>>>> taken care by it).
>>>>
>>>> Is there any 'correct' way to do that in PETSc?
>>>>
>>>> Thanks in advance,
>>>>
>>>> Alejandro
>>>>
>>>
>>
>


-- 
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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