Hi dear community,
I am trying to solve a simple PDE system in the form of:
where Na, ni are functions of [x,t] and va, vi, beta are constant coefficients. I have no problem solving the system with IC and non-periodic BC:
Na[x,0]=Na0; Na[0,t]=Na0;
ni[x,0]=ni0; ni[0,t]=ni0
However, when trying to implement a periodic boundary condition for ni:
ni[0,t]=ni[L,t]
and keeping the BC for Na the left boundary non-periodic: Na[0,t]=Na0 Mathematica states that such a combination is not allowed: 
Has anybody encountered such a problem and has found a workaround for mixing periodic and non-periodic boundary conditions?
