Factor complexity of S-adic words generated by the Arnoux–Rauzy–Poincaré algorithm

The Arnoux–Rauzy–Poincaré multidimensional continued fraction algorithm is obtained by combining the Arnoux–Rauzy and Poincaré algorithms. It is a generalized Euclidean algorithm. Its three-dimensional linear version consists in subtracting the sum of the two smallest entries from the largest if possible (Arnoux–Rauzy step), and otherwise, in subtracting the smallest entry from the median and the median from the largest (the Poincaré step), and by performing when possible Arnoux–Rauzy steps in priority. After renormalization it provides a piecewise fractional map of the standard 2-simplex. We study here the factor complexity of its associated symbolic dynamical system, defined as an S-adic system. It is made of infinite words generated by the composition of sequences of finitely many substitutions, together with some restrictions concerning the allowed sequences of substitutions expressed in terms of a regular language. Here, the substitutions are provided by the matrices of the linear version of the algorithm. We give an upper bound for the linear growth of the factor complexity. We then deduce the convergence of the associated algorithm by unique ergodicity.