© 1979 by London Mathematical Society
Lyapunov'S Method Applied to the Hopf Bifurcation
Department of Pure Mathematics and Mathematical Statistics 16 Mill Lane, Cambridge CB2 1SB
In principle, it is possible to prove the existence and stability of a stable periodic orbit of a set of differential equations by finding a Lyapunov function for it. However, this is usually only practicable for orbits with a particularly simple form. In this paper we first show how a sufficiently good approximation to an exact Lyapunov function can still be used to prove existence of an orbit, though we are not able to determine local uniqueness or stability by our method. Then we show how to construct such an approximation in the case of the orbit produced by the Hopf bifurcation: our method gives a new derivation of the standard formula for the quantity whose sign determines the direction of bifurcation.