1. Introduction to Nonlinear Differential and Integral Equation;Davis,1962
2. Numerical study of periodic solutions of the Van der Pol equation;Urabe,1963
3. The method of matched asymptotic expansions for the periodic solution of the Van der Pol equation;Bavinck;Int. J. Non-Linear Mech.,1974
4. Perturbation Methods;Nayfeh,1973
5. Nonlinear Vibrations in Mechanical and Electrical Systems;Stoker,1950