Minimal weight expansions in Pisot bases

Christiane Frougny (1) , Wolfgang Steiner (1)

1 LIAFA - Laboratoire d'informatique Algorithmique : Fondements et Applications

For applications to cryptography, it is important to represent numbers with a small number of non-zero digits (Hamming weight) or with small absolute sum of digits. The problem of finding representations with minimal weight has been solved for integer bases, e.g. by the non-adjacent form in base~2. In this paper, we consider numeration systems with respect to real bases $\beta$ which are Pisot numbers and prove that the expansions with minimal absolute sum of digits are recognizable by finite automata. When $\beta$ is the Golden Ratio, the Tribonacci number or the smallest Pisot number, we determine expansions with minimal number of digits $\pm1$ and give explicitely the finite automata recognizing all these expansions. The average weight is lower than for the non-adjacent form.

Mots clés: minimal weight; beta-expansions; Pisot numbers; Fibonacci numbers; automata

Domaines: Mathématique discrète [cs.DM]; Théorie des nombres [math.NT]; Cryptographie et sécurité [cs.CR]

Christiane Frougny, Wolfgang Steiner. Minimal weight expansions in Pisot bases. Journal of Mathematical Cryptology, 2008, 2 (4), pp.365-392. ⟨10.1515/JMC.2008.017⟩. ⟨hal-00265661v3⟩