title: Variational principle for limit cycles of the Rayleigh-van der Pol equation.
abstract: We show that the amplitude of the limit cycle of Rayleigh's equation can be obtained from a variational principle. We use this principle to reobtain the asymptotic values for the period and amplitude of the Rayleigh and van der Pol equations. Limit cycles of general Liénard systems can also be derived from a variational principle.
authors.affiliation: Facultad de Física, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22, Chile.
authors.forename: R D
authors.initials: RD
authors.lastname: Benguria
authors.forename: M C
authors.initials: MC
authors.lastname: Depassier