[petsc-users] Inquiry regarding DMAdaptLabel function

[Zongze Yang]

Hi, Matt

Thanks for your clarification. Can I change the type of DMPlex to DMForest?

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/>
>
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