Diophantine approximation of the orbits of any given point under the family of beta-transformations
摘要
This paper is concerned with the Diophantine properties of the orbits of any given point under beta-transformations as beta varies. More precisely, let Tβ be the beta-transformation with parameter β > 1 and ϕ: ℕ → [0, 1] be a non-negative function. It is shown that for any given point z ∈ (0, 1], for almost all or almost no parameters β > 1, the orbit of z under Tβ can be ϕ-well approximated by a given sequence {xn}n≥1 infinitely many times according to the divergence or convergence of the series Σϕ(n) This can be viewed as a Duffin–Schaeffer type problem for the action of β-transformations compared with the action of irrational rotations. The new fundamental properties and the method presented here can also be applied to problems in beta-expansion with a fixed β.