On the period function of Liénard systems

Abstract

We study the period functionTof a centerOof a Liénard system. A sufficient condition for the monotonicity ofT, or for the isochronicity ofO, is given. Such a condition is also necessary whenfandgare analytic, andgis odd. In this case a characterization of isochronous centers of Liénard systems is given. Strict monotonicity and global monotonicity ofTare also investigated. © 1999 Academic Press.