ON THE PERIOD FUNCTION OF LIENARD SYSTEMS

Abstract We study the period functionTof a centerOof a Lienard 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 Lienard systems is given. Strict monotonicity and global monotonicity ofTare also investigated.

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