[petsc-users] local to global mapping for DMPlex

[Matthew Knepley]

On Wed, Dec 20, 2017 at 11:08 AM, Yann JOBIC <yann.jobic at univ-amu.fr> wrote:

> On 12/19/2017 05:50 PM, Matthew Knepley wrote:
>
> On Tue, Dec 19, 2017 at 11:40 AM, Yann JOBIC <yann.jobic at univ-amu.fr>
> wrote:
>
>> Hello,
>>
>> We want to extract the cell connectivity from a DMPlex. We have no
>> problem for a sequential run.
>>
>
> Do you want it on disk? If so, you can just DMView() for HDF5. That
> outputs the connectivity in a global numbering.
> I can show you the calls I use inside if you want.
>
> I looked at the code, specifically DMPlexWriteTopology_Vertices_H
> DF5_Static
> cellIS should have what i want.
> However it seems that it is not the case. Do i look at the right spot in
> the code ?
>

cellIS has the entire connectivity. You sound like you want cell-vertex
only. You could get that by just

  DMPlexUninterpolate(dm, &udm);
  <get your cellIS from udm>
  DMDestroy(&udm);


> I also looked at DMPlexGetCellNumbering, which does exactly what i want
> for the global numbering of Cells, even if the ordering is different for
> different number of processors.
>

Yes.


> When i use DMPlexGetVertexNumbering, i've got negative values, which is
> correctly handeled by DMPlexWriteTopology_Vertices_HDF5_Static, but i
> really don't understand this part.
>

There are no shared cells in your partition, so you get all positive
numbers. You have shared vertices, so the negative numbers are for vertices
you do not own. If the negative number is n, the corresponding global
number is -(n+1). Notice that the transformation is 1-1 and its square is I.


> I succeed in having the coordinates, but maybe not in the right order. I
> reused DMPlexWriteCoordinates_HDF5_Static, which create a Vec of vertex
> coordinates, but i couldn't understand the order of vertex coordinate
> linked (or not) with DMPlexWriteTopology_Vertices_HDF5_Static. The number
> of local coordinates is also strange, and does not correspond to the cell's
> topology.
>

It matches the order of the global numbering.

  Thanks

    Matt


> Thanks for the help!
>
> Regards,
>
> Yann
>
>
> I usually put
>
>   DMViewFromOptions(dm, NULL, "-dm_view")
>
> Then
>
>   -dm_view hdf5:mesh.h5
>
>   Thanks,
>
>     Matt
>
>
>> However for parallel ones, we need to get the node numbering in the
>> global ordering, as when we distribute the mesh, we only have local nodes,
>> and thus local numbering.
>>
>> It seems that we should use DMGetLocalToGlobalMapping (we are using
>> Fortran with Petsc 3.8p3). However, we get the running error :
>>
>> [0]PETSC ERROR: No support for this operation for this object type
>> [0]PETSC ERROR: DM can not create LocalToGlobalMapping
>>
>> Is it the right way to do it ?
>>
>> Many thanks,
>>
>> Regards,
>>
>> Yann
>>
>>
>
>
> --
> 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.caam.rice.edu/%7Emk51/>
>
>
>


-- 
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.caam.rice.edu/~mk51/>
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