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

Matteo Semplice matteo.semplice at uninsubria.it
Mon May 2 11:22:55 CDT 2022


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

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.


> 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
> -- 
> 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/ 
> <https://eur01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.cse.buffalo.edu%2F~knepley%2F&data=05%7C01%7Cmatteo.semplice%40uninsubria.it%7Cba6f4499929f45d75a5f08da2c55e259%7C9252ed8bdffc401c86ca6237da9991fa%7C0%7C0%7C637871044633599928%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=DRvIjjr1cjHWdoSpQJr9UkIWVxlopKbKt%2BW5sQBvQE4%3D&reserved=0>

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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