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Classification of the centers and their isochronicity for a class of polynomial differential systems of arbitrary degree

2011; Elsevier BV; Volume: 227; Issue: 1 Linguagem: Inglês

10.1016/j.aim.2011.02.003

1090-2082

Jaume Llibre, Clàudìa Valls,

Nonlinear Waves and Solitons

In this paper we classify the centers localized at the origin of coordinates, and their isochronicity for the polynomial differential systems in R2 of degree d that in complex notation z=x+iy can be written asz˙=(λ+i)z+Az(d−n+1)/2z¯(d+n−1)/2+Bz(d+n+1)/2z¯(d−n−1)/2+Cz(d+1)/2z¯(d−1)/2+Dz(d−(2+j)n+1)/2z¯(d+(2+j)n−1)/2, where j is either 0 or 1. If j=0 then d⩾5 is an odd integer and n is an even integer satisfying 2⩽n⩽(d+1)/2. If j=1 then d⩾3 is an integer and n is an integer with converse parity with d and satisfying 0<n⩽[(d+1)/3] where [⋅] denotes the integer part function. Furthermore λ∈R and A,B,C,D∈C. Note that if d=3 and j=0, we are obtaining the generalization of the polynomial differential systems with cubic homogeneous nonlinearities studied in K.E. Malkin (1964) [17], N.I. Vulpe and K.S. Sibirskii (1988) [25], J. Llibre and C. Valls (2009) [15], and if d=2, j=1 and C=0, we are also obtaining as a particular case the quadratic polynomial differential systems studied in N.N. Bautin (1952) [2], H. Zoladek (1994) [26]. So the class of polynomial differential systems here studied is very general having arbitrary degree and containing the two more relevant subclasses in the history of the center problem for polynomial differential equations.