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Planar real polynomial differential systems of degree \(n> 3\) having a weak focus of high order. (English) Zbl 1254.34048

The authors construct polynomial systems of degree \(n>3\), which for even \(n\) have a week focus of order \(n^2-1\) and for odd \(n\) have a week focus of order \((n^2-1)/2\) at the origin. The systems are from the family of the form \[ \dot x=-y(1-f_\alpha(x,y))+P(x,y), \;\dot y=x(1-f_\alpha(x,y))+Q(x,y), \] where \( f_\alpha(x,y) \) is a real homogeneous polynomial of degree \(n-1\) depending on the real parameter \(\alpha\), \(P\) and \(Q\) are homogeneous polynomials of degree \(n\) with small real coefficients. The obtained result improves previously known estimates.

MSC:

34C05 Topological structure of integral curves, singular points, limit cycles of ordinary differential equations
34C07 Theory of limit cycles of polynomial and analytic vector fields (existence, uniqueness, bounds, Hilbert’s 16th problem and ramifications) for ordinary differential equations

References:

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