Differential Equations(Continuous Time Models) differential equation is a mathematical equation that relates some function with its derivatives. An equation contains only ordinary derivates of one or more dependent variables of a single independent variable. For Example, PDE(PARTIAL DIFFERENTIAL EQUATION An equation contains partial derivates of one or more dependent variables of two or more independent variables. For Example, Difference Equations(Discrete-Time Models) The finite-difference methods are numerical methods for solving differential equations approximating them with difference equations, in which finite differences approximate the derivatives. The finite element methods are numerical techniques for finding approximate solutions to boundary value problems for partial differential equations