## Abstract

For 0 ≤ α ≤ 1 given, we consider the one-parameter family of α-continued fraction maps, which include the Gauss map (α = 1), the nearest integer (α = 1 / 2) and by-excess (α = 0) continued fraction maps. To each of these expansions and to each choice of a positive function u on the interval I_{α} we associate a generalized Brjuno function B_{(α, u)} (x). When α = 1 / 2 or α = 1, and u (x) = - log (x), these functions were introduced by Yoccoz in his work on linearization of holomorphic maps. We compare the functions obtained with different values of α and we prove that the set of (α, u)-Brjuno numbers does not depend on the choice of α provided that α ≠ 0. We then consider the case α = 0, u (x) = - log (x) and we prove that x is a Brjuno number (for α ≠ 0) if and only if both x and - x are Brjuno numbers for α = 0.

Original language | English |
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Pages (from-to) | 24-41 |

Number of pages | 18 |

Journal | Journal of Approximation Theory |

Volume | 162 |

Issue number | 1 |

DOIs | |

Publication status | Published - 2010 Jan |

Externally published | Yes |

## Keywords

- Approximations of real numbers
- Brjuno function
- Continued fractions

## ASJC Scopus subject areas

- Analysis
- Numerical Analysis
- Mathematics(all)
- Applied Mathematics