[petsc-users] What exactly goes into DMPlexSetRefinementLimit

[Justin Chang]

Because the base mesh starts off with 6 elements and 8 vertices. This is
enough data for one cell per MPI process. Refinement is done after
DMPlexDistribute(...). If I use anymore than 6 cores, some of the MPI ranks
will have an empty DM Object. For example:

$ mpirun -n 8 --bind-to-core --bysocket ./ex12 -dim 3 -run_type full
-interpolate 1 -petscspace_order 1 -bc_type dirichlet -ksp_rtol 1.0e-7
-pc_type ml -refinement_limit 1 -dm_refine 1 -dm_view

DM Object: Parallel Mesh 8 MPI processes

  type: plex

Parallel Mesh in 3 dimensions:

  0-cells: 10 0 10 10 10 0 10 10

  1-cells: 25 0 25 25 25 0 25 25

  2-cells: 24 0 24 24 24 0 24 24

  3-cells: 8 0 8 8 8 0 8 8

Labels:

  marker: 1 strata of sizes (18)

  depth: 4 strata of sizes (10, 25, 24, 8)

Number of SNES iterations = 1

L_2 Error: 0.118178

On Wed, Aug 17, 2016 at 2:28 PM, Matthew Knepley <knepley at gmail.com> wrote:

> On Wed, Aug 17, 2016 at 2:04 PM, Justin Chang <jychang48 at gmail.com> wrote:
>
>> When I enter values  like 1/16, 1/12, 1/24, and so on, I was expecting to
>> get roughly the same dm object as if I simply did -dm_refine <0/1/2/3>.
>> Instead it seems I get highly unstructured grids, and the smaller the
>> number gets, the fewer additional cells I get. Is there a way to make the
>> refinement limit uniform?
>>
>
> Why not just use -dm_refine ?
>
>    Matt
>
>
>> On Wed, Aug 17, 2016 at 9:38 AM, Matthew Knepley <knepley at gmail.com>
>> wrote:
>>
>>> On Wed, Aug 17, 2016 at 5:23 AM, Justin Chang <jychang48 at gmail.com>
>>> wrote:
>>>
>>>> Hi all,
>>>>
>>>> Playing around with SNES ex12.c and I am attempting to tinker around
>>>> with 3D options. I am trying to understand what kind of values go into
>>>> -refinement_limit for 3D simplices.
>>>>
>>>
>>> The cell volume limits for any cells created out of the existing cells.
>>> This is how TetGen understands refinement. I think a
>>> better way is to use a metric tensor field, and we now have an interface
>>> to pragmatic for this (I think currently I only hooked it up
>>> to DMCoarsen() but it does both). Clearly the interface is immature, but
>>> this is the way we are headed.
>>>
>>>   Matt
>>>
>>>
>>>> Thanks,
>>>> Justin
>>>>
>>>
>>>
>>>
>>> --
>>> 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
>>>
>>
>>
>
>
> --
> 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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