SEARCH Articles Figures Tables Differential equations order Differential equations partial Differential order First order hyperbolic partial differential equations First order parabolic partial differential equation Order equation Partial Ordering Partial differential Partial differential equation first-order linear Partial differential equation higher orders Partial differential equation second-order linear Partial differential equations first order Partial differential equations linear second-order hyperbolic Partial equation Second order hyperbolic partial differential equations Second order partial differential equation Second-order partial differential equations and Greens functions