[petsc-users] Numbering of DMPlexGetCellNumbering

[Matthew Knepley]

On Thu, Mar 7, 2013 at 3:56 PM, Garnet Vaz <garnet.vaz at gmail.com> wrote:

> Hi,
>
> For an small distributed unstructured mesh  with overlap 1
> which is *not* interpolated yet, if I do a DMPlexGetCellNumbering()
> I obtain an IS as follows:
>
> [0] Number of indices in set 6
> [0] 0 -6
> [0] 1 0
> [0] 2 -8
> [0] 3 1
> [0] 4 2
> [0] 5 3
> [1] Number of indices in set 6
> [1] 0 4
> [1] 1 5
> [1] 2 6
> [1] 3 -1
> [1] 4 7
> [1] 5 -4.
>
> Running the same example but by DMPlexInterpolate() and then
> DMPlexGetCellNumbering() provides instead the output:
>
> [0] Number of indices in set 6
> [0] 0 0
> [0] 1 1
> [0] 2 2
> [0] 3 3
> [0] 4 4
> [0] 5 5
> [1] Number of indices in set 6
> [1] 0 6
> [1] 1 7
> [1] 2 8
> [1] 3 9
> [1] 4 10
> [1] 5 11
>

There is something wrong with this result. It has to do with the order in
which you created
things. Right now, I do not have DMInterpolate() update the communication
structures, since
it would involve coordination between processes. Thus you should call
DMInterpolate()
before DMDistribute().

  Thanks,

     Matt


> The former result I find very useful since it provides the number of
> ghost cells on each processor (the negative IS values) and moreover
> the negative IS values also indicate the global numbering of the
> ghost cells. Eg: On the first processor the cell 0 is a ghost cell with
> its global numbering 5.
>
> The behavior of DMPlexGetCellNumbering() after the interpolation does
> not bother me but I would like to know in the former case if the output
> is the right output i.e, it is not merely a side effect which might get
> changed later on.
>
> Thank You.
>
> --
> Regards,
> Garnet
>



-- 
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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