[petsc-users] Uninterpolating a distributed mesh

[Matthew Knepley]

On Mon, Apr 20, 2015 at 6:09 AM, Justin Chang <jchang27 at uh.edu> wrote:

> 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.
>

I have finally fixed this. It is in next.

  Thanks,

     Matt


> 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
>



-- 
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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