Periodic Boundary Condition + Constant

[mtrautner]

I'm looking to enforce a constraint like u[x,1] = u[x,0] + f0(t) and u[0,y] = u[1,y] + f1(t) for some given functions f0 and f1 for all x and y on a 2D square. It seems like dolfinx_mpc is the closest to achieving such a constraint. Do you have an idea of which functions I might modify to make this happen? Thanks.

[jorgensd]

I did make a try at this a while back. It should work with very minor modifications, like:

https://github.com/jorgensd/dolfinx_mpc/blob/main/cpp/lifting.h#L260

Is there. It is only in lifting the constant becomes relevant, thus only minor modifications is needed. I'll see if I can find the mathematical derivation i did on this (late next week).

[mtrautner]

Okay thanks. If I have this right, the commented out lines 260~264 of what you linked subtract a constant times some matrix values from relevant entities of the linear system, so the idea would be to instead just add a constant in this spot?

[RFurze]

Were you able to get this modification working? I'm looking to implement precisely this kind of constraint in what sounds like a similar multiscale model.