[petsc-users] extract arbitrary subset of a DMDA

[Randall Mackie]

Hi Matteo,

Take a look at these posts from a few years ago and see if they will help you:

https://lists.mcs.anl.gov/pipermail/petsc-users/2021-January/043037.html 

https://lists.mcs.anl.gov/pipermail/petsc-users/2021-January/043043.html 

We were able to use this approach to extract a sub-region of a DMDA, and it should be possible for you to do so as well.


Good luck,

Randy M.


> On Oct 10, 2025, at 6:48 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?
> 
> 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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