Matrix representations of fourth order boundary value problems with periodic boundary conditions

We show that a class of regular self-adjoint fourth order boundary value problems (BVPs) is equivalent to a certain class of matrix problems. Conversely, for any given matrix problem in this class, there exist fourth order self-adjoint BVPs which are equivalent to the given matrix problem. Equivalent here means that they have exactly the same eigenvalues. Such an equivalence is considered with the special coupled boundary conditions, i.e. periodic boundary conditions.