PURELY PERIODIC BETA-EXPANSIONS OVER LAURENT SERIES

The aim of this paper is to characterize the formal power series which have purely periodic β-expansions in Pisot or Salem unit base under some condition. Furthermore, we will prove that if β is a quadratic Pisot unit base, then every rational f in the unit disk has a purely periodic β-expansion and discuss their periods.

Tilings Generated by Ito-Sadahiro and Balanced (-ß)-numeration Systems

Let β > 1 be a cubic Pisot unit. We study forms of Thurston tilings arising from the classical β-numeration system and from the (−β)-numeration system for both the Ito-Sadahiro and balanced definition of the (−β)-transformation.

Infinite special branches in words associated with beta-expansions

International audience A Parry number is a real number β > 1 such that the Rényi β-expansion of 1 is finite or infinite eventually periodic. If this expansion is finite, β is said to be a simple Parry number. Remind that any Pisot number is a Parry number. In a previous work we have determined the complexity of the fixed point uβ of the canonical substitution associated with β-expansions, when β is a simple Parry number. In this paper we consider the case where β is a non-simple Parry number. We determine the structure of infinite left special branches, which are an important tool for the computation of the complexity of uβ. These results allow in particular to obtain the following characterization: the infinite word uβ is Sturmian if and only if β is a quadratic Pisot unit.

Connectedness of number theoretical tilings

International audience Let T=T(A,D) be a self-affine tile in \reals^n defined by an integral expanding matrix A and a digit set D. In connection with canonical number systems, we study connectedness of T when D corresponds to the set of consecutive integers \0,1,..., |det(A)|-1\. It is shown that in \reals^3 and \reals^4, for any integral expanding matrix A, T(A,D) is connected. We also study the connectedness of Pisot dual tilings which play an important role in the study of β -expansion, substitution and symbolic dynamical system. It is shown that each tile generated by a Pisot unit of degree 3 is arcwise connected. This is naturally expected since the digit set consists of consecutive integers as above. However surprisingly, we found families of disconnected Pisot dual tiles of degree 4. Also we give a simple necessary and sufficient condition for the connectedness of the Pisot dual tiles of degree 4. As a byproduct, a complete classification of the β -expansion of 1 for quartic Pisot units is given.

ON THE CONTEXT-FREENESS OF THE θ-EXPANSIONS OF THE INTEGERS

Let θ>1 be a nonintegral real number such that the θ-expansion of every positive integer is finite. If the set of θ-expansions of all the positive integers is a context-free language, then θ must be a quadratic Pisot unit. Résumé: Soit θ>1 un nombre réel non entier tel que le θ-développement de tout entier positif soit fini. Si l'on suppose que l'enslembe des θ-développements des entiers positifs forme un langage algébrique, alors θ doit être un nombre de Pisot quadratique unitaire.