[petsc-users] Uninterpolating a distributed mesh

[Justin Chang]

Matt,

I have attempted to implement this, called UninterpolateSF(), and attached
is the code for the function. However, I suspect that there are bugs
because when I refine the mesh via -dm_refine my program crashes.

In my program I have the following lines for uninterpolating a distributed
mesh:

DM idm=NULL;
ierr = DMPlexUninterpolate(*dm, &idm);CHKERRQ(ierr);
ierr = DMPlexCopyCoordinates(*dm, idm);CHKERRQ(ierr);
ierr = DMPlexCopyLabels(*dm, idm);CHKERRQ(ierr);
if (size>1) {
  ierr = UninterpolateSF(*dm,idm);CHKERRQ(ierr);
}
ierr = DMDestroy(dm);CHKERRQ(ierr);
*dm = idm;

Can you have a look into the source code I attached and see what may
potentially be the issue?

Thanks,


On Mon, Apr 13, 2015 at 4:28 PM, Matthew Knepley <knepley at gmail.com> wrote:

> On Mon, Apr 13, 2015 at 4:22 PM, Justin Chang <jchang27 at uh.edu> wrote:
>
>> Is there an example somewhere that does something similar to this?
>>
>
> There is DMPlexShiftSF_Internal() in plexsubmesh.c
>
>   Matt
>
>
>> Thanks,
>>
>> On Mon, Apr 13, 2015 at 12:31 PM, Matthew Knepley <knepley at gmail.com>
>> wrote:
>>
>>> On Sat, Apr 11, 2015 at 6:55 PM, Justin Chang <jchang27 at uh.edu> wrote:
>>>
>>>> Hello,
>>>>
>>>> When I call DMPlexUninterpolate(...) on a distributed mesh (say 2
>>>> processors), it seems to overwrite the "ghost" points (i.e., the points not
>>>> locally owned by the processor) and treats all points as if they are local
>>>> to the processor.
>>>>
>>>
>>> Yes, I wrote Uninterpolate() just for testing, and do not currently
>>> handle the SF. I put it on my TODO list.
>>>
>>> Its not hard if you want to try. You just filter out any points that are
>>> not cells and vertices from the SF, so
>>>
>>>   PetscSFGetGraph()
>>>   for (leaves)
>>>     if leaf not a cell or vertex, skip
>>>   PetscSFSetGraph()
>>>
>>>   Thanks,
>>>
>>>     Matt
>>>
>>>
>>>> Say I have this 2D cell-vertex mesh:
>>>>
>>>> 14----15-----16
>>>> | \  5  | \ 7   |
>>>> |   \   |   \   |
>>>> |  4  \ |  6  \ |
>>>> 11----12-----13
>>>> | \  1  | \ 3   |
>>>> |   \   |   \   |
>>>> |  0  \ |  2  \ |
>>>> 8------9------10
>>>>
>>>> Which results in the following DM:
>>>>
>>>> DM Object: 2 MPI processes
>>>>   type: plex
>>>> DM_0x84000004_0 in 2 dimensions:
>>>>   0-cells: 9 0
>>>>   2-cells: 8 0
>>>> Labels:
>>>>   marker: 1 strata of sizes (8)
>>>>   depth: 2 strata of sizes (9, 8)
>>>>
>>>> I proceed by interpolating this DM:
>>>>
>>>> DM Object: 2 MPI processes
>>>>   type: plex
>>>> DM_0x84000004_1 in 2 dimensions:
>>>>   0-cells: 9 0
>>>>   1-cells: 16 0
>>>>   2-cells: 8 0
>>>> Labels:
>>>>   marker: 1 strata of sizes (16)
>>>>   depth: 3 strata of sizes (9, 16, 8)
>>>>
>>>> Then distributing across 2 processors:
>>>>
>>>> DM Object:Parallel Mesh 2 MPI processes
>>>>   type: plex
>>>> Parallel Mesh in 2 dimensions:
>>>>   0-cells: 6 6
>>>>   1-cells: 9 9
>>>>   2-cells: 4 4
>>>> Labels:
>>>>   marker: 1 strata of sizes (9)
>>>>   depth: 3 strata of sizes (6, 9, 4)
>>>>
>>>> I have the option of uniformly refining the mesh here but I choose not
>>>> to for now. If my dofs are vertex based, then the global size of my DM
>>>> vector is 9 and the local sizes for ranks 0 and 1 are 3 and 6 respectively.
>>>> However, if I choose to uninterpolate the mesh by calling
>>>> DMPlexUninterpolate(...), I get this:
>>>>
>>>> DM Object: 2 MPI processes
>>>>   type: plex
>>>> DM_0x84000004_2 in 2 dimensions:
>>>>   0-cells: 6 6
>>>>   2-cells: 4 4
>>>> Labels:
>>>>   marker: 1 strata of sizes (5)
>>>>   depth: 2 strata of sizes (6, 4)
>>>>
>>>> And the global size of my DM vector becomes 12 and the local size for
>>>> both ranks is 6. It looks like the ghost points in rank 0 have been
>>>> duplicated, which is not suppose to happen.
>>>>
>>>> Is there a way to capture the ghost point information when
>>>> uninterpolating the DM?
>>>>
>>>> Thanks,
>>>>
>>>> --
>>>> Justin Chang
>>>> PhD Candidate, Civil Engineering - Computational Sciences
>>>> University of Houston, Department of Civil and Environmental Engineering
>>>> Houston, TX 77004
>>>> (512) 963-3262
>>>>
>>>
>>>
>>>
>>> --
>>> 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
>>>
>>
>>
>>
>> --
>> Justin Chang
>> PhD Candidate, Civil Engineering - Computational Sciences
>> University of Houston, Department of Civil and Environmental Engineering
>> Houston, TX 77004
>> (512) 963-3262
>>
>
>
>
> --
> 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
>



-- 
Justin Chang
PhD Candidate, Civil Engineering - Computational Sciences
University of Houston, Department of Civil and Environmental Engineering
Houston, TX 77004
(512) 963-3262
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