[petsc-users] Inquiry regarding DMAdaptLabel function

[Matthew Knepley]

On Mon, Feb 27, 2023 at 9:45 AM Zongze Yang <yangzongze at gmail.com> wrote:

> Hi, Matt
>
> Thanks for your clarification. Can I change the type of DMPlex to DMForest?
>

You can, however DMForest is for structured adaptive meshes using
quadtrees, and I do not believe
Firedrake works with that.

  Thanks,

    Matt


> Best wishes,
> Zongze
>
>
> On Mon, 27 Feb 2023 at 20:18, Matthew Knepley <knepley at gmail.com> wrote:
>
>> On Sat, Feb 18, 2023 at 2:25 AM Zongze Yang <yangzongze at gmail.com> wrote:
>>
>>> Dear PETSc Group,
>>>
>>> I am writing to inquire about the function DMAdaptLabel in PETSc.
>>> I am trying to use it coarse a mesh, but the resulting mesh is refined.
>>>
>>> In the following code, all of the `adpat` label values were set to 2
>>> (DM_ADAPT_COARSEN).
>>> There must be something wrong. Could you give some suggestions?
>>>
>>
>> Sorry for the late reply. You are right, I need to put in error messages
>> for this. Here is what is happening.
>> PETSc tries to fallback if you do not have certain packages. In this
>> case, you are not using DMForest,
>> which responds to both coarsen and refine, so the
>> mesh generator interprets all markers as refine (they
>> cannot coarsen). I will add a check that fails on the coarsen marker.
>>
>> Coarsening is much more difficult in the presence of boundaries, which is
>> why it is not implemented in
>> most packages. For unstructured coarsening, I do not think there is any
>> choice but MMG.
>>
>>   Thanks,
>>
>>      Matt
>>
>> ```python
>>> from firedrake import *
>>> from firedrake.petsc import PETSc
>>>
>>> def mark_all_cells(mesh):
>>>     plex = mesh.topology_dm
>>>     with PETSc.Log.Event("ADD_ADAPT_LABEL"):
>>>         plex.createLabel('adapt')
>>>         cs, ce = plex.getHeightStratum(0)
>>>         for i in range(cs, ce):
>>>             plex.setLabelValue('adapt', i, 2)
>>>
>>>     return plex
>>>
>>> mesh = RectangleMesh(10, 10, 1, 1)
>>>
>>> x = SpatialCoordinate(mesh)
>>> V = FunctionSpace(mesh, 'CG', 1)
>>> f = Function(V).interpolate(10 + 10*sin(x[0]))
>>> triplot(mesh)
>>>
>>> plex = mark_all_cells(mesh)
>>> new_plex = plex.adaptLabel('adapt')
>>> mesh = Mesh(new_plex)
>>> triplot(mesh)
>>> ```
>>>
>>> Thank you very much for your time.
>>>
>>> Best wishes,
>>> Zongze
>>>
>>
>>
>> --
>> 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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