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Permutation of values of irrationality measure functions

Number Theory 2026-04-01 v1

Abstract

For an irrational number αR\alpha\in\mathbb{R} we consider its irrationality measure function ψα(t)=min1qt,qZqα. \psi_\alpha(t) = \min_{1\le q\le t,\, q\in\mathbb{Z}} \| q\alpha \|. Let α=(α1,,αn)\boldsymbol{\alpha} = (\alpha_1, \dots, \alpha_n) be nn-tuple of pairwise independent irrational numbers. For each tR>1t \in \mathbb{R}_{>1} irrationality measure functions ψα1,,ψαn\psi_{\alpha_1}, \dots, \psi_{\alpha_n} can be written in an increasing order ψαv1(t)>ψαv2(t)>>ψαvn1(t)>ψαvn(t).\psi_{\alpha_{v_1}}(t) > \psi_{\alpha_{v_2}}(t) > \dots > \psi_{\alpha_{v_{n-1}}}(t) > \psi_{\alpha_{v_n}}(t). We consider the vector of functions vα(t):R>1Sn\boldsymbol{v}_{\boldsymbol{\alpha}}(t): \mathbb{R}_{>1} \rightarrow S_n associated to this order and defined as vα(t)=(v1,v2,,vn1,vn).\boldsymbol{v}_{\boldsymbol{\alpha}}(t) = ( v_1, v_2, \dots, v_{n-1}, v_n ). Let k(α)\boldsymbol{k}(\boldsymbol{\alpha}) be the number of infinitely occurring different values of vα(t)\boldsymbol{v}_{\boldsymbol{\alpha}}(t). It is known that if k(α)=k\boldsymbol{k}(\boldsymbol{\alpha})= k we have nk(k+1)2. n \leq \frac{k(k+1)}{2}. At the same time, for k3k \geq 3 and n=k(k+1)2n = \frac{k(k+1)}{2} there exists an nn-tuple α\boldsymbol{\alpha} with k(α)=k\boldsymbol{k}(\boldsymbol{\alpha}) = k. In this work we define a kk-cyclic permutation π\pi and prove that in the extremal case n=k(k+1)2, k(α)=kn = \frac{k(k+1)}{2}, \ \boldsymbol{k}(\boldsymbol{\alpha}) = k the set of successive values of vα(t)\boldsymbol{v}_{\boldsymbol{\alpha}}(t) is an orbit of π\pi.

Keywords

Cite

@article{arxiv.2507.20416,
  title  = {Permutation of values of irrationality measure functions},
  author = {Victoria Rudykh},
  journal= {arXiv preprint arXiv:2507.20416},
  year   = {2026}
}

Comments

22 pages, 10 figures