Stability of the Denjoy-Wolff theorem

Argyrios Christodoulou¹ ; Ian Short²

¹ Queen Mary University of London, School of Mathematical Sciences
² The Open University, School of Mathematics and Statistics

Annales Fennici Mathematici, Tome 46 (2021) no. 1, pp. 421-431.

Résumé

  The Denjoy-Wolff theorem is a foundational result in complex dynamics, which describes the dynamical behaviour of the sequence of iterates of a holomorphic self-map $f$ of the unit disc $\mathbf{D}$. Far less well understood are nonautonomous dynamical systems $F_n=f_n\circ f_{n-1} \circ \dots \circ f_1$ and $G_n=g_1\circ g_{2} \circ \dots \circ g_n$, for $n=1,2,\ldots$, where $f_i$ and $g_j$ are holomorphic self-maps of $\mathbf{D}$. Here we obtain a thorough understanding of such systems $(F_n)$ and $(G_n)$ under the assumptions that $f_n\to f$ and $g_n\to f$. We determine when the dynamics of $(F_n)$ and $(G_n)$ mirror that of $(f^n)$, as specified by the Denjoy-Wolff theorem, thereby providing insight into the stability of the Denjoy-Wolff theorem under perturbations of the map $f$.

Détail

Keywords: Denjoy-Wolff theorem, holomorphic map, hyperbolic metric