[petsc-users] Using DMDA for a block-structured grid approach

[Mark Adams]

Let me backup a bit.
I think you have an application that has a Cartesian, or a least fine, grid
and you "have to implement a block structured grid approach".
Is this block structured solver well developed?
We have support for block structured (quad-tree) grids you might want to
use. This is a common approach for block structured grids.

Thanks,
Mark



On Mon, Jun 26, 2023 at 12:08 PM Barry Smith <bsmith at petsc.dev> wrote:

>
>
> > On Jun 26, 2023, at 11:44 AM, Srikanth Sathyanarayana <srcs at mpcdf.mpg.de>
> wrote:
> >
> > Dear PETSc developers,
> >
> >
> > I am currently working on a Gyrokinetic code where I essentially have to
> implement a block structured grid approach in one of the subdomains of the
> phase space coordinates. I have attached one such example in the x -
> v_parallel subdomains where I go from a full grid to a grid based on 4
> blocks (divided along x direction) which is still Cartesian but misaligned
> across blocks (the grid is a very coarse representation). So the idea is to
> basically create a library for the existing solver and try to implement the
> block structured grid approach which mainly involves some sort of
> interpolation between the blocks to align the points.
> >
> >
> > I came up with an idea to implement this using DMDA. I looked into the
> old threads where you have suggested using DMComposite in order to tackle
> such problems although a clear path for the interpolation between the DM's
> was not clarified. Nonetheless, my main questions were:
> >
> > 1. Do you still suggest using DMComposite to approach this problem.
>
>   Unfortunately, that is all we have for combining DM's. You can use
> unstructured, or structured or unstructed with quad-tree-type refinement
> but we don't have a "
> canned" approach for combining a bunch of structured grids together
> efficiently and cleanly (lots of issues come up in trying to design such a
> thing in a distributed memory environment since some blocks may need to
> live on different number of MPI ranks)
> >
> > 2. Is there a way to use DMDA where the user provides the allocation? My
> main problem is that I am not allowed to change the solvers data structure
>
>    The allocation for what?
> >
> > 3. I looked into VecCreateMPIWithArray for the user provided allocation,
> however I am not very sure if this Vector can be used with the DMDA
> operations.
>
>    Yes, you can use these variants to create vectors that you use with
> DMDA; so long as they have the correct dimensions.
> >
> >
> > Overall, I request you to please let me know what you think of this
> approach (using DMDA) and I would be grateful if you could suggest me any
> alternatives.
> >
> >
> > Thanks and regards,
> >
> > Srikanth
> > <Screenshot from 2023-06-26 17-24-32.png>
>
>
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