[petsc-users] Periodic boundary conditions in DMPlex

[Matthew Knepley]

On Fri, Oct 15, 2021 at 7:08 AM Pierre Seize <pierre.seize at onera.fr> wrote:

> Hi,
>
> I'm writing a code using PETSc to solve NS equations with FV on an
> unstructured mesh. Therefore I use DMPlex.
>
> Regarding periodicity, I manage to implement it this way:
>
>    - for each couple of boundaries that is linked with periodicity, I
> create a buffer vector with an ISLocalToGlobalMapping
>
>    - then, when I need to fill the ghost cells corresponding to the
> periodicity, the i "true" cell of the local vector fills the buffer
> vector on location i with VecSetValuesBlockedLocal, then
> VecAssemblyBegin/VecAssemblyEnd ensure each value is send to the correct
> location thanks to the mapping, then the i "ghost" cell of the local
> vector reads the vector on location i to get it's value.
>
>
> It works, but it seems to me there is a better way, with maybe PetscSF,
> VecScatter, or something I don't know yet. Does anyone have any advice ?
>

There are at least two other ways to handle this. First, the method that is
advocated in
Plex is to actually make a periodic geometry, meaning connect the cells
that are meant
to be connected. Then, if you partition with overlap = 1,
PetscGlobalToLocal() will fill in
these cell values automatically.

Second, you could use a non-periodic geometry, but alter the LocalToGlobal
map such
that the cells gets filled in anyway. Many codes use this scheme and it is
straightforward
with Plex just by augmenting the map it makes automatically.

Does this make sense?

  Thanks,

     Matt


> Pierre Seize
>
-- 
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/>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20211015/ba283a67/attachment.html>