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The period functions' higher order derivatives

Abstract

We prove a formula for the nn-th derivative of the period function TT in a period annulus of a planar differential system. For n=1n = 1, we obtain Freire, Gasull and Guillamon formula for the period's first derivative \cite{FGG}. We apply such a result to hamiltonian systems with separable variables and other systems. We give some sufficient conditions for the period function of conservative second order O.D.E.'s to be convex.Comment: 2 figure

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