[petsc-dev] Will DMPlexDistribute only ever distribute Cells?

[Matthew Knepley]

On Thu, Apr 16, 2020 at 9:28 PM Jacob Faibussowitsch <jacob.fai at gmail.com>
wrote:

> What do you want to do?
>
> Count the global number of points per depth based on all_reduce’ing the
> maximum positive value returned from the IS’s listed below. This works as
> intended for anything but cells since global number of points = max(IS) +
> 1. For cells this breaks since 1 rank reports 3 as max, the next reports 6,
> etc.
>

I do not understand this at all. This algorithm does not work for any
stratum. For example, suppose that we have a straight line of quad cells,
1 per process. The vertices would be [1, 5) on all processes but there
would be 2*(P + 1) vertices.

  Thanks,

     Matt


>  The system should be flexible enough to distribute whatever you want
>
> What is the best way to check that a non-standard distribute has been
> done?
>
> Best regards,
>
> Jacob Faibussowitsch
> (Jacob Fai - booss - oh - vitch)
> Cell: (312) 694-3391
>
> On Apr 16, 2020, at 8:17 PM, Matthew Knepley <knepley at gmail.com> wrote:
>
> On Thu, Apr 16, 2020 at 9:04 PM Jacob Faibussowitsch <jacob.fai at gmail.com>
> wrote:
>
>> Hello All,
>>
>> TL;DR: Is it possible now, or is it a planned feature, for plex to
>> distribute over anything but points with height = 0?
>>
>> If I understand this correctly when plex currently partitions a graph,
>> points with height 0 are only owned by a single process, but all other
>> points can be co-owned by multiple procs.  For example for a 2D plex with 8
>> vertices, 12 edges, and 6 cells over 2 procs these are the global-local
>> IS’s for all points on processes (negative values indicate ownership by
>> another proc) the final IS corresponding to cells will always have positive
>> values as each proc is the sole owner of its cells.
>>
>
> What do you want to do? The system should be flexible enough to distribute
> whatever you want, but the current guarantee
> is that the cone of any points is always available. So if you decide to
> distribute something else, like faces, then it ends up
> looking just like an overlapping mesh with some custom overlap. Moreover,
> the dual mesh only really makes sense for cells.
> For faces/edges you would need a hypergraph partitioner.
>
>   Thanks,
>
>      Matt
>
>
>> *VERTICES*
>> IS Object: 2 MPI processes
>>   type: general
>> [0] Number of indices in set 7
>> [0] 0 -2
>> [0] 1 0
>> [0] 2 -3
>> [0] 3 -4
>> [0] 4 -5
>> [0] 5 -6
>> [0] 6 -8
>> [1] Number of indices in set 7
>> [1] 0 1
>> [1] 1 2
>> [1] 2 3
>> [1] 3 4
>> [1] 4 5
>> [1] 5 6
>> [1] 6 7
>>
>> *EDGES*
>> IS Object: 2 MPI processes
>>   type: general
>> [0] Number of indices in set 9
>> [0] 0 0
>> [0] 1 1
>> [0] 2 -4
>> [0] 3 -5
>> [0] 4 -6
>> [0] 5 2
>> [0] 6 -7
>> [0] 7 -9
>> [0] 8 -11
>> [1] Number of indices in set 9
>> [1] 0 3
>> [1] 1 4
>> [1] 2 5
>> [1] 3 6
>> [1] 4 7
>> [1] 5 8
>> [1] 6 9
>> [1] 7 10
>> [1] 8 11
>>
>> *CELLS*
>> IS Object: 2 MPI processes
>>   type: general
>> [0] Number of indices in set 3
>> [0] 0 0
>> [0] 1 1
>> [0] 2 2
>> [1] Number of indices in set 3
>> [1] 0 3
>> [1] 1 4
>> [1] 2 5
>>
>> Best regards,
>>
>> Jacob Faibussowitsch
>> (Jacob Fai - booss - oh - vitch)
>> Cell: (312) 694-3391
>>
>>
>
> --
> 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.cse.buffalo.edu/~knepley/>
>
>
>

-- 
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.cse.buffalo.edu/~knepley/>
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