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Discrete part of the second Lagrange spectrum

Number Theory 2023-04-28 v1

Abstract

Given an irrational number α\alpha consider its irrationality measure function ψα(t)=min1qt,qZqα\psi_{\alpha}(t)=\min\limits_{1\le q\le t, q\in\mathbb{Z}}\|q\alpha\|. The set of all values of λ(α)=(lim supttψα(t))1\lambda(\alpha)=(\limsup\limits_{t\to\infty} t\psi_{\alpha}(t))^{-1} where α\alpha runs through the set RQ\mathbb{R}\setminus\mathbb{Q} is called the Lagrange spectrum L\mathbb{L}. In a paper by Moshchevitin an irrationality measure function ψα[2](t)=min1qt,qZ,qqiqα\psi^{[2]}_{\alpha}(t)=\min\limits_{1\le q\le t, q\in\mathbb{Z},q\ne q_i}\|q\alpha\| was introduced. In other words, we consider the best approximations by fractions, whose denominators are not the denominators of the convergents to α\alpha. Replacing the function ψα\psi_{\alpha} in the definition of L\mathbb{L} by ψα[2]\psi^{[2]}_{\alpha}, one can get a set L2\mathbb{L}_2 which is called the ''second'' Lagrange spectrum. In this paper we give the complete structure of discrete part of L2\mathbb{L}_2.

Cite

@article{arxiv.2304.13872,
  title  = {Discrete part of the second Lagrange spectrum},
  author = {Dmitry Gayfulin},
  journal= {arXiv preprint arXiv:2304.13872},
  year   = {2023}
}

Comments

9 pages

R2 v1 2026-06-28T10:19:09.754Z