An Exponential Method for the Solution of Systems of Ordinary Differential Equations An explicit, coupled, single-step method for the numerical solution of initial value problems for systems of ordinary differential equations is presented. The method was designed to be general purpose in nature but to be especially efficient when dealing with stiff systems of differential equations. It is, in general, second order except for the case of a linear system with constant coefficients and linear forcing terms; in that case, the method is third order. It has been implemented and put to routine usage in biological applications-where stiffness frequently appears-with favorable results. When compared to a standard fourth order Runge-Kutta implementation, computation time required by this method has ranged from comparable for certain nonstiff problems to better than two orders of magnitude faster for some highly stiff systems. CACM December, 1974 Chu, S. C. Berman, M. numerical solution, ordinary differential equations, initial value problems, stiff systems 5.17 CA741207 JB January 13, 1978 4:20 PM 2567 4 2567 2567 4 2567 2268 5 2567 2567 5 2567 2567 5 2567 2567 5 2567 755 5 2567