Analysis of Duffing's oscillator equation with time-dependent parameters

In this study, an undamped Duffing's oscillator equation with time-dependent parameters has been considered. The time-varying part is expanded in a series of ultraspherical polynomials in the spirit of Sinha and Chou and only the constant part is retained. The non-linearity parameter is assumed to be small so that the number of iterations required is only two. The results compare well with those obtained by the Runge-Kutta fourth order method. (C) 200