EXPFIT4 - a Fortran program for the numerical solution of systems of nonlinear second-order initial-value problems. We present a FORTRAN program which solves the initial-value problem associated with nonstiff systems of the form y ” =f(x,y). The program is based on a family of exponential-fitted four-step methods. The presented code is particularly suited to solve second-order initial-value problems arising from physics. (Source: http://cpc.cs.qub.ac.uk/summaries/)