nonisochronous

Using the correction of a vector field to characterize isochronicity and explicit computations of this quantity for polynomial vector fields, wa are able to describe a very large class of nonisochronous Hamiltonian system of even degree of degree arbitrary large.

2016, Jacky Cresson, Jordy Palafox, “Isochronous centers of polynomial Hamiltonian systems and a conjecture of Jarque and Villadelprat”, in arXiv