[petsc-users] What exactly goes into DMPlexSetRefinementLimit

[Matthew Knepley]

On Wed, Aug 17, 2016 at 2:35 PM, Justin Chang <jychang48 at gmail.com> wrote:

> 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:
>

You could

1) Just stick an explicit call to uniform refinement in for the serial mesh

2) Use a cell volume that is 1/N, where N is the number of cells you want

   Matt


> $ 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
>>
>
>


-- 
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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