Evolutionary Problems Involving Sturm-Liouville Operators
  The purpose of this paper is to further exemplify an approach to evolutionary problems originally developed in earlier works for a special case and later extended to more general evolutionary problems. We are here concerned with the $(1+1)$ -dimensional evolutionary case, which in a particular case results in a hyperbolic partial differential equation with a Sturm-Liouville type spatial operator constrained by an impedance type boundary condition. 
Rainer Picard and Bruce Watson
math.AP