Natural extensions and Gauss measures for piecewise homographic continued fractions
[Extensions naturelles et mesures de Gauss pour des algorithmes de fraction continues homographiques par morceaux]
Bulletin de la Société Mathématique de France, Tome 147 (2019) no. 3, pp. 515-544

We give a heuristic method to solve explicitly for an absolutely continuous invariant measure for a piecewise differentiable, expanding map of a compact subset I of Euclidean space d. The method consists of constructing a skew product family of maps on I×d, which has an attractor. Lebesgue measure is invariant for the skew product family restricted to this attractor. Under reasonable measure-theoretic conditions, integration over the fibers gives the desired measure on I. Furthermore, the attractor system is then the natural extension of the original map with this measure. We illustrate this method by relating it to various results in the literature.

Nous donnons une méthode heuristique pour trouver explicitement une mesure invariante absolument continue pour une application différentiable par morceaux et expansive d’un sous-ensemble compact I de l’espace euclidien d. La méthode consiste à construire une famille d’applications qui est un produit croisé sur I×d, et à montrer que cette famille possède un attracteur. La mesure de Lebesgue est par construction invariante pour la restriction à l’attracteur de cette famille d’applications. Sous des hypothèses raisonnables sur la mesure, l’intégration le long des fibres donne la mesure invariante cherchée sur I. De plus, le système construit sur l’attracteur est l’extension naturelle de l’application originale, munie de cette mesure invariante. Nous illustrons cette méthode par plusieurs exemples tirés de la littérature.

DOI : 10.24033/bsmf.2791
Classification : 37E05, 11K50, 37A45
Keywords: natural extensions, continued fractions, invariant measures, iterated function system
Mots-clés : extension naturelle, fractions continues, mesures invariantes, systèmes de fonctions itérées

Arnoux, Pierre 1 ; Schmidt, Thomas A. 2

1 Université d’Aix-Marseille et CNRS, Institut de Mathématiques de Marseille (UMR7373), Site Sud, Campus de Luminy, Case 907, 13288 MARSEILLE Cedex 9 France
2 Department of Mathematics, Oregon State University Corvallis, OR 97331
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Arnoux, Pierre; Schmidt, Thomas A. Natural extensions and Gauss measures for piecewise homographic continued fractions. Bulletin de la Société Mathématique de France, Tome 147 (2019) no. 3, pp. 515-544. doi: 10.24033/bsmf.2791

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