Self-sustained oscillations of dynamical and stochastic systems and their mathematical image — an attractor

In the present paper autonomous and nonautonomous oscillations of dynamical and stochastic systems are analyzed in the framework of common concepts. The definition of an attractor is introduced for a nonautonomous system. The definitions of self-sustained oscillations and a self-sustained oscillatory system is proposed, that generalize A. A. Andronov's concept introduced for autonomous systems with one degree of freedom.