“…In contrast to the perturbation methods, the nonperturbation methods do not use any small or artificial parameter. Examples include Adomian decomposition method [29], Homotopy analysis method [30], Variational iteration method [31], Energy balance method [2] and its modifications [32][33][34], He Chengtian's interpolation method [27] also called max-min approach, amplitude-frequency formulation [35], Hamiltonian approach [36], global error minimization method [37], Harmonic balance method [4] and its modifications [38][39][40][41][42], cubication methods [43][44][45][46], variational methods [47][48][49], differential transform method [50], and continuous piecewise linearization method [8]. Nonperturbation methods also have various limitations.…”