A Mathematica program for the approximate analytical solution to a nonlinear undamped Duffing equation by a new approximate approach
Keywords: نوسانگر غیرخطی; 02.30.Hq; 02.60.Cb; 02.70.-cUndamped Duffing equation; Approximate analytical solution; Nonlinear second-order ordinary differential equation; High-accurate methods; Nonlinear oscillator; Harmonic balance method