[petsc-users] extract arbitrary subset of a DMDA

[Matthew Knepley]

On Fri, Oct 10, 2025 at 9:48 AM Matteo Semplice via petsc-users <
petsc-users at mcs.anl.gov> wrote:

> Dear all,
>
>      I am wondering if there is a way to extract a subset of a DMDA and
> use it as a mesh. The use case is to program a finite-difference method
> in which the domain is defined by a levelset function: if I could
> completely ignore the parts of the background DMDA that are "far away"
> from the object, I guess I would avoid some cores having almost no
> workload. I figure that I could setup a DMDA, load/compute the levelset
> on the entire box, then mark the nodes to be retained, extract the
> submesh and repartition it. I would also need a mean to transfer some
> Vec data from the DMDA to the new mesh.
>
> I guess that the extracted mesh would then become a DMPlex and it would
> not retain any DMDA flavour (like notions of which are the grid nodes
> sitting on top/bottom, left/right of a given node), right?
>

If you are planning on extracting a Plex anyway, I think it would be easier
to just
start with a Cartesian Plex, instead of a DA, and use DMPlexCreateSubmesh().

  Thanks,

     Matt


> Thanks
>
>      Matteo
>
> --
> Prof. Matteo Semplice
> Università degli Studi dell’Insubria
> Dipartimento di Scienza e Alta Tecnologia – DiSAT
> Professore Associato
> Via Valleggio, 11 – 22100 Como (CO) – Italia
> tel.: +39 031 2386316
>
>

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