Determination of limit cycles by iterated homotopy perturbation method for nonlinear oscillators with strong nonlinearity (Q949140)

Consider the perturbed equation \[ u''+\varepsilon f(u,u')+ u= 0,\tag{\(*\)} \] where \(\varepsilon\) is a sufficiently small parameter and \(f:\mathbb{R}\times \mathbb{R}\to \mathbb{R}\) is sufficiently smooth. The authors apply He's iterated homotopy perturbation method to approximate periodic solutions of \((*)\).