At the International Symposium The Impact of Chaos on Science and Society organized by the United Nations University and the University of Tokyo in 1991, Prof. Yoshisuke Ueda presented a paper entitled Strange Attractors and Origin of Chaos.

At present, people say that the data I was collecting with my analog computer on 27 November 1961, is the oldest example of chaos discovered in a second-order nonautonomous periodic system. Around the same time, it was Lorenz who made the discovery of chaos in a third-order autonomous system this is how Prof. Ueda began his talk.

Ueda considered a nonlinear oscillator governed by the second-order ordinary differential equation subjected to periodic excitation. In fact, both researchers, Ueda and Lorenz, studied a three-dimensional dynamical system with continuous time, and their interest was focused on the evolution of the solution in time.

In that time, about 1961, Ueda worked as a postgraduate student at the University of Tokyo under supervision of Prof. C.Hayashi. The question he tried to answer was: what types of steady-state oscillations can occur in nonlinear driven oscillators? The expected steady-states were first calculated by means of the analytical approximate methods. Consequently, student Ueda was supposed to obtain simulation results that confirm the theoretical ones. It happened that, just on that day in November 1961, the oscillation phenomena portrayed by the analog computer did not agree with the expected, regular results. The approximate theoretical calculations predicted that the results should be mapped in the form of smooth, closed curves, whereas...