### Symmetry, Integrability and Geometry: Methods and Applications (SIGMA)

SIGMA 14 (2018), 085, 27 pages      arXiv:1803.06537      https://doi.org/10.3842/SIGMA.2018.085

### Renormalization of the Hutchinson Operator

Yann Demichel
Laboratoire MODAL'X - EA3454, Université Paris Nanterre, 200 Avenue de la République, 92000 Nanterre, France

Received March 20, 2018, in final form August 10, 2018; Published online August 16, 2018

Abstract
One of the easiest and common ways of generating fractal sets in ${\mathbb R}^D$ is as attractors of affine iterated function systems (IFS). The classic theory of IFS's requires that they are made with contractive functions. In this paper, we relax this hypothesis considering a new operator $H_\rho$ obtained by renormalizing the usual Hutchinson operator $H$. Namely, the $H_\rho$-orbit of a given compact set $K_0$ is built from the original sequence $\big(H^n(K_0)\big)_n$ by rescaling each set by its distance from $0$. We state several results for the convergence of these orbits and give a geometrical description of the corresponding limit sets. In particular, it provides a way to construct some eigensets for $H$. Our strategy to tackle the problem is to link these new sequences to some classic ones but it will depend on whether the IFS is strictly linear or not. We illustrate the different results with various detailed examples. Finally, we discuss some possible generalizations.

Key words: Hutchinson operator; iterated function system; attractor; fractal sets.

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