Other Useful References
Nonlinear Dynamics and Chaos, J.M.T. Thompson
and H.B. Stewart, John Wiley & Sons, 1986.
Nonlinear Oscillations, Dynamical Systems, and
Bifurcations of Vector Fields, by J. Guckenheimer and P. Holmes, Springer,
Nonlinear Oscillations in Physical Systems,
by C. Hayashi, Princeton University press, 1985.
Chaotic Vibrations: an Introduction to Chaotic
Dynamics for Applied Scientists and Engineers, by F. C. Moon, Wiley,
for other references: see http://www-chaos.umd.edu/