Homoclinic Tangles for Noninvertible Maps
Nonlinear Analysis 41 (2000) 259–276 www.elsevier.nl/locate/na Homoclinic tangles for noninvertible maps Evelyn Sander Department of Mathematical Sciences, George Mason University, MS 3F2, 4400 University Drive, Fairfax, VA 22030, USA Received 2 March 1998; accepted 17 July 1998 Keywords: Homoclinic tangles; Noninvertible maps; Transverse homoclinic point 1. Introduction Not all naturally occurring iterated systems have the property that time is reversible. In which case, the dynamics must be modelled by a noninvertible map rather than by a di eomorphism. While one-dimensional theory describes dynamics of noninvertible maps, higher-dimensional theory has focussed on di eomorphisms, though there are many higher-dimensional examples of natural systems modelled by noninvertible maps. For example, noninvertible maps occur in the study of population dynamics [2], time one maps of delay equations [25], control theory algorithms [1, 5, 6], neural networks [16], and iterated di erence methods [14]. In order to use dynamical systems theory in applications for which maps are noninvertible, it is important to know how the theory di ers from the di eomorphism case. One of the principal indications of chaotic dynamics in deterministic systems is the existence of transverse homoclinic orbits. This paper examines the existence of homoclinic tangles and the associated dynamic behavior for noninvertible maps. In particular, we give examples of maps which have transverse intersection of stable and unstable manifolds but no horseshoe. Furthermore, we show that this is a codimension two phenomenon. Papers by Steinlein and Walther [24,25] and Lerman and Shil’nikov [13] both estab- lish conditions for a transverse homoclinic point of a noninvertible map to be contained in a horseshoe.
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