MOLFiniteDifference periodic boundaries

[ChrisRackauckas]

https://discourse.julialang.org/t/periodic-boundary-conditions-for-pde-system-using-modellingtoolkit-and-diffeqbase/51827/3

[valentinsulzer]

What do you suggest for syntax?

[ChrisRackauckas]

I'd hope we could just do the natural syntax, i.e. u(0,t) ~ u(1,t) and such.

[ChrisRackauckas]

SciML/DiffEqOperators.jl#301 is going to come up here.

[xtalax]

Closed by #34