Abstract

Abstract We study behavior of the topological entropy as the function of parameters for two-parameter family of symmetric Lorenz maps T c,ɛ (x) = (−1 + c|x| 1−ɛ ) · sgn(x). This is the normal form for splitting the homoclinic loop in systems which have a saddle equilibrium with one-dimensional unstable manifold and zero saddle value. Due to L.P. Shilnikov results, such a bifurcation corresponds to the birth of Lorenz attractor (when the saddle value becomes positive). We indicate those regions in the bifurcation plane where the topological entropy depends monotonically on the parameter c, as well as those for which the monotonicity does not take place. Also, we indicate the corresponding bifurcations for the Lorenz attractors.

Highlights

  • The paper is devoted to the study of one-dimensional factor map for the geometric model of Lorenz attractors in the form of two-parameter family of Lorenz maps on the interval I = [−1, 1] given by

  • 1. 0 < c ≤ 2, which guarantees the invariance of the interval I; 2. 0 < ε < 1, which corresponds to positive saddle value in the geometric Lorenz model and implies infinite one-sided derivatives at the discontinuity point

  • Applied Mathematics and Nonlinear Sciences 5(2020) 293–306. Such families of maps appear naturally in the studies of bifurcations related to the birth of Lorenz attractor from the separatrix loop with zero saddle value

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Summary

Introduction

Applied Mathematics and Nonlinear Sciences 5(2020) 293–306 Such families of maps appear naturally in the studies of bifurcations related to the birth of Lorenz attractor from the separatrix loop with zero saddle value. One of the results of those studies is the following fact: in the parameter plane (α, λ ), the boundary of the region corresponding to the existence of Lorenz attractor, contains the system having homoclinic figure-8 loop at a saddle with zero saddle value We show that in the case when Tc,ε is expanding ( (DT ≥ q > 1), the topological entropy is monotone increasing in c

Bifurcation diagram
Non-monotonicity of the topological entropy

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