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

[Lawrence Mitchell]

> 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?

Lawrence
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