English

Julia sets of random exponential maps

Dynamical Systems 2020-05-20 v1

Abstract

For a sequence (λn)(\lambda_n) of positive real numbers we consider the exponential functions fλn(z)=λnezf_{\lambda_n} (z) = \lambda_n e^z and the compositions Fn=fλnfλn1...fλ1F_n = f_{\lambda_n} \circ f_{\lambda_{n-1}} \circ ... \circ f_{\lambda_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 (λn)(\lambda_n). Among other results, we prove the Julia set for a random sequence {λn}\{\lambda_n \}, chosen uniformly from a neighbourhood of 1e\frac{1}{e}, is the whole plane with probability 11. We also prove the Julia set for 1e+1np\frac{1}{e} + \frac{1}{n^p} is the whole plane for p<12p < \frac{1}{2}, and give an example of a sequence {λn}\{\lambda_n \} for which the iterates of 00 converge to infinity starting from any index, but the Fatou set is non-empty.

Keywords

Cite

@article{arxiv.2005.09469,
  title  = {Julia sets of random exponential maps},
  author = {Krzysztof Lech},
  journal= {arXiv preprint arXiv:2005.09469},
  year   = {2020}
}
R2 v1 2026-06-23T15:39:40.516Z