[petsc-users] [petsc-maint] How to impose boundary conditions using DMDA

[Matthew Knepley]

On Mon, Oct 29, 2018 at 6:22 AM Lawrence Mitchell <wencel at gmail.com> wrote:

>
>
> On 29 Oct 2018, at 10:09, Matthew Knepley <knepley at gmail.com> wrote:
>
> On Mon, Oct 29, 2018 at 5:39 AM Fengwen Wang <fwan at mek.dtu.dk> wrote:
> Hi Matt and Barry,
>
> I only have  a regular 2D  square domain of a unit cell.
>
> The boundary condition implies some sort of topology. For example, if you
> condition was
>
>   u, v (x = 0) = u, v (x = 1)
>
> you are on a cylinder. And if you add
>
>   u, v (y = 0) = u, v (y = 1)
>
> you are on a torus. However, you are hooking the right edge to the top edge
> and also transforming the basis. I cannot understand what is meant.
>
>
> I'm no good at drawing embedded things, I read the bc like the attached
> picture. You sort of fold the top and right edges together "inwards", which
> means that stuff that flows out of the right edge flows in through the top
> edge, and stuff that is flowing up along the right edge ends up flowing
> left along the top edge?
>

You can certainly map the right edge to the top edge (its topologically a
square again), but that
mapping is not smooth, and I do not know how you would make a global basis
for the approximation space.

   Matt


> Lawrence
>


-- 
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/>
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