Im trying to solve Helmholtz equation
\nabla ^2u(r,\phi,z) + k^2u(r,\phi,z) = 0
in a hollow cylinder with length L and a < r < b
and the boundary conditions:
u(a,\phi,z) = F(\phi,z)
u(b,\phi,z) = G(\phi,z)
u(r,\phi,0) = P(\phi,z)
u(r,\phi,L) = Q(\phi,z)...