References
- Bellman , R. 1972 . Perturbation Techniques in Mathematics, Engineering and Physics , Dover/Constable .
- McLachlan , N. W. 1950 . Ordinary Non‐Linear Differential Equations in Engineering and Physical Sciences , second edition , Oxford . 1956
- Stoker , J. J. 1950 . Nonlinear Vibrations in Mechanical and Electrical Systems , Inter‐science .
- Struble , R. A. 1962 . Nonlinear Differential Equations , McGraw‐Hill .