Re: [petsc-users] different periodicity per dof in DMDA?

[Matteo Semplice]

Thanks!

On 02/05/2022 18:07, Matthew Knepley wrote:
On Mon, May 2, 2022 at 11:25 AM Matteo Semplice 
<matteo.sempl...@uninsubria.it> wrote:

    Hi.

    I am facing a PDE with 2 dofs per node in which one dof has periodic
    b.c. in the x direction and the other one periodic b.c. in the y
    direction. Is there a (possibly quick-and-dirty) solution to
    represent
    this in a DM (not necessarily a DMDA)?


I am trying to understand what this means.

It comes from a toy model for more complicated quantum field theory 
model that's hard for me to understand.

Usually we think of periodicity as arising from the domain, not the field.

I think it would be easiest to:

  a) Use two different DMDA for the fields that "match up" where needed

This is kind of what I was thinking at. So I would create two DMDA, then 
a DMComposite with the two and finally create Vecs and Matrices from the 
DMComposite?

If so, then how do I assemble matrices for linear systems? If I extract 
submatrices, I could use MatSetValuesStencil on diagonal blocks, but how 
about the off-diagonal ones? These latter would have rows/cols indexed 
by different DMDAs.

Matteo


or

  b) Use a DMStag since it sounds like these should live on horizontal 
and vertical edges

  Thanks,

     Matt

    I understand the request it's strange, but I should add that we are
    experimenting numerically with this toy model, so in fact the b.c.
    may
    change in the future... just to stress once more that I am not
    after a
    perfect solution, but anything that would at least allow parallel
    runs
    with few processors would do for now.

    Thanks in advance

         Matteo



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