Pii: S0168-9274(98)00129-9

Three new Runge–Kutta methods are presented for numerical integration of systems of linear inhomogeneous ordinary differential equations (ODEs) with constant coefficients. Such ODEs arise in the numerical solution of partial differential equations governing linear wave phenomena. The restriction to linear ODEs with constant coefficients reduces the number of conditions which the coefficients of the Runge–Kutta method must satisfy. This freedom is used to develop methods which are more efficient than conventional Runge–Kutta methods. A fourthorder method is presented which uses only two memory locations per dependent variable, while the classical fourth-order Runge–Kutta method uses three. This method is an excellent choice for simulations of linear wave phenomena if memory is a primary concern. In addition, fifthand sixth-order methods are presented which require five and six stages, respectively, one fewer than their conventional counterparts, and are therefore more efficient. These methods are an excellent option for use with high-order spatial discretizations.  1999 Elsevier Science B.V. and IMACS. All rights reserved.