Julia sets of random exponential maps

Krzysztof Lech

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arXiv · 2005.09469

Julia sets of random exponential maps

Krzysztof Lech

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Abstract

For a sequence $(λ_n)$ of positive real numbers we consider the exponential functions $f_{λ_n} (z) = λ_n e^z$ and the compositions $F_n = f_{λ_n} \circ f_{λ_{n-1}} \circ ... \circ f_{λ_1}$. For such a non-autonomous family we can define the Fatou and Julia sets analogously to the usual case of autonomous iteration. The aim of this document is to study how the Julia set depends on the sequence $(λ_n)$. Among other results, we prove the Julia set for a random sequence $\{λ_n \}$, chosen uniformly from a neighbourhood of $\frac{1}{e}$, is the whole plane with probability $1$. We also prove the Julia set for $\frac{1}{e} + \frac{1}{n^p}$ is the whole plane for $p < \frac{1}{2}$, and give an example of a sequence $\{λ_n \} $ for which the iterates of $0$ converge to infinity starting from any index, but the Fatou set is non-empty.

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Krzysztof Lech. 2020-05-19. Julia sets of random exponential maps. https://arxiv.org/abs/2005.09469

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