Mathematics Department, University of North Texas, 1155 Union Cir #311430, Denton, TX 76203-5017, USA |
For a positive integer $ M $ and a real base $ q\in(1, M+1] $, let $ {\mathcal{U}}_q $ denote the set of numbers having a unique expansion in base $ q $ over the alphabet $ \{0, 1, \dots, M\} $, and let $ \mathbf{U}_q $ denote the corresponding set of sequences in $ \{0, 1, \dots, M\}^ {\mathbb{N}} $. Komornik et al. [ Adv. Math. 305 (2017), 165–196] showed recently that the Hausdorff dimension of $ {\mathcal{U}}_q $ is given by $ h(\mathbf{U}_q)/\log q $, where $ h(\mathbf{U}_q) $ denotes the topological entropy of $ \mathbf{U}_q $. They furthermore showed that the function $ H: q\mapsto h(\mathbf{U}_q) $ is continuous, nondecreasing and locally constant almost everywhere. The plateaus of $ H $ were characterized by Alcaraz Barrera et al. [ Trans. Amer. Math. Soc., 371 (2019), 3209–3258]. In this article we reinterpret the results of Alcaraz Barrera et al. by introducing a notion of composition of fundamental words, and use this to obtain new information about the structure of the function $ H $. This method furthermore leads to a more streamlined proof of their main theorem.
| [1] |
R. Alcaraz Barrera,
Topological and ergodic properties of symmetric sub-shifts, Discrete Contin. Dyn. Syst., 34 (2014), 4459-4486.
doi: 10.3934/dcds.2014.34.4459. |
| [2] |
R. Alcaraz Barrera, S. Baker and D. Kong,
Entropy, topological transitivity, and dimensional properties of unique $q$-expansions, Trans. Amer. Math. Soc., 371 (2019), 3209-3258.
doi: 10.1090/tran/7370. |
| [3] |
P. Allaart, S. Baker and D. Kong, Bifurcation sets arising from non-integer base expansions, in J. Fractal Geom., (2018), arXiv: 1706.05190. |
| [4] |
P. Allaart and D. Kong, On the continuity of the Hausdorff dimension of the univoque set, Advances in Mathematics, 354 (2019), 106729, arXiv: 1804.02879.
doi: 10.1016/j.aim.2019.106729. |
| [5] |
P. Allaart and D. Kong, Relative bifurcation sets and the local dimension of univoque bases, preprint, 2018, arXiv: 1809.00323. |
| [6] |
S. Baker, Generalized golden ratios over integer alphabets, Integers, 14 (2014), 28 pp. |
| [7] |
M. de Vries and V. Komornik,
Unique expansions of real numbers, Adv. Math., 221 (2009), 390-427.
doi: 10.1016/j.aim.2008.12.008. |
| [8] |
P. Erdős, M. Horváth and I. Joó,
On the uniqueness of the expansions $1=\sum q^{-n_i}$, Acta Math. Hungar., 58 (1991), 333-342.
doi: 10.1007/BF01903963. |
| [9] |
P. Erdős and I. Joó,
On the number of expansions $1=\sum q^{-n_i}$, Ann. Univ. Sci. Budapest. Eötvös Sect. Math., 35 (1992), 129-132.
|
| [10] |
P. Erdős, I. Joó and V. Komornik,
Characterization of the unique expansions $1=\sum_{i=1}^\infty q^{-n_i}$ and related problems, Bull. Soc. Math. France, 118 (1990), 377-390.
doi: 10.24033/bsmf.2151. |
| [11] |
P. Glendinning and T. Hall,
Zeros of the kneading invariant and topological entropy for Lorenz maps, Nonlinearity, 9 (1996), 999-1014.
doi: 10.1088/0951-7715/9/4/010. |
| [12] |
P. Glendinning and N. Sidorov,
Unique representations of real numbers in non-integer bases, Math. Res. Lett., 8 (2001), 535-543.
doi: 10.4310/MRL.2001.v8.n4.a12. |
| [13] |
V. Komornik, D. Kong and W. X. Li,
Hausdorff dimension of univoque sets and devil's staircase, Adv. Math., 305 (2017), 165-196.
doi: 10.1016/j.aim.2016.03.047. |
| [14] |
V. Komornik and P. Loreti,
Unique developments in non-integer bases, Amer. Math. Monthly, 105 (1998), 636-639.
doi: 10.1080/00029890.1998.12004937. |
| [15] |
V. Komornik and P. Loreti,
Subexpansions, superexpansions and uniqueness properties in non-integer bases, Period. Math. Hungar., 44 (2002), 197-218.
doi: 10.1023/A:1019696514372. |
| [16] |
D. Kong and W. X. Li,
Hausdorff dimension of unique beta expansions, Nonlinearity, 28 (2015), 187-209.
doi: 10.1088/0951-7715/28/1/187. |
| [17] |
D. Kong, W. X. Li and F. M. Dekking,
Intersections of homogeneous Cantor sets and beta-expansions, Nonlinearity, 23 (2010), 2815-2834.
doi: 10.1088/0951-7715/23/11/005. |
| [18] |
D. Lind and B. Marcus, An Introduction to Symbolic Dynamics and Coding, Cambridge University Press, Cambridge, 1995.
doi: 10.1017/CBO9780511626302.
|
| [19] |
W. Parry,
On the $\beta$-expansions of real numbers, Acta Math. Acad. Sci. Hungar., 11 (1960), 401-416.
doi: 10.1007/BF02020954. |
| [20] |
A. Rényi,
Representations for real numbers and their ergodic properties, Acta Math. Acad. Sci. Hungar., 8 (1957), 477-493.
doi: 10.1007/BF02020331. |
show all references
| [1] |
R. Alcaraz Barrera,
Topological and ergodic properties of symmetric sub-shifts, Discrete Contin. Dyn. Syst., 34 (2014), 4459-4486.
doi: 10.3934/dcds.2014.34.4459. |
| [2] |
R. Alcaraz Barrera, S. Baker and D. Kong,
Entropy, topological transitivity, and dimensional properties of unique $q$-expansions, Trans. Amer. Math. Soc., 371 (2019), 3209-3258.
doi: 10.1090/tran/7370. |
| [3] |
P. Allaart, S. Baker and D. Kong, Bifurcation sets arising from non-integer base expansions, in J. Fractal Geom., (2018), arXiv: 1706.05190. |
| [4] |
P. Allaart and D. Kong, On the continuity of the Hausdorff dimension of the univoque set, Advances in Mathematics, 354 (2019), 106729, arXiv: 1804.02879.
doi: 10.1016/j.aim.2019.106729. |
| [5] |
P. Allaart and D. Kong, Relative bifurcation sets and the local dimension of univoque bases, preprint, 2018, arXiv: 1809.00323. |
| [6] |
S. Baker, Generalized golden ratios over integer alphabets, Integers, 14 (2014), 28 pp. |
| [7] |
M. de Vries and V. Komornik,
Unique expansions of real numbers, Adv. Math., 221 (2009), 390-427.
doi: 10.1016/j.aim.2008.12.008. |
| [8] |
P. Erdős, M. Horváth and I. Joó,
On the uniqueness of the expansions $1=\sum q^{-n_i}$, Acta Math. Hungar., 58 (1991), 333-342.
doi: 10.1007/BF01903963. |
| [9] |
P. Erdős and I. Joó,
On the number of expansions $1=\sum q^{-n_i}$, Ann. Univ. Sci. Budapest. Eötvös Sect. Math., 35 (1992), 129-132.
|
| [10] |
P. Erdős, I. Joó and V. Komornik,
Characterization of the unique expansions $1=\sum_{i=1}^\infty q^{-n_i}$ and related problems, Bull. Soc. Math. France, 118 (1990), 377-390.
doi: 10.24033/bsmf.2151. |
| [11] |
P. Glendinning and T. Hall,
Zeros of the kneading invariant and topological entropy for Lorenz maps, Nonlinearity, 9 (1996), 999-1014.
doi: 10.1088/0951-7715/9/4/010. |
| [12] |
P. Glendinning and N. Sidorov,
Unique representations of real numbers in non-integer bases, Math. Res. Lett., 8 (2001), 535-543.
doi: 10.4310/MRL.2001.v8.n4.a12. |
| [13] |
V. Komornik, D. Kong and W. X. Li,
Hausdorff dimension of univoque sets and devil's staircase, Adv. Math., 305 (2017), 165-196.
doi: 10.1016/j.aim.2016.03.047. |
| [14] |
V. Komornik and P. Loreti,
Unique developments in non-integer bases, Amer. Math. Monthly, 105 (1998), 636-639.
doi: 10.1080/00029890.1998.12004937. |
| [15] |
V. Komornik and P. Loreti,
Subexpansions, superexpansions and uniqueness properties in non-integer bases, Period. Math. Hungar., 44 (2002), 197-218.
doi: 10.1023/A:1019696514372. |
| [16] |
D. Kong and W. X. Li,
Hausdorff dimension of unique beta expansions, Nonlinearity, 28 (2015), 187-209.
doi: 10.1088/0951-7715/28/1/187. |
| [17] |
D. Kong, W. X. Li and F. M. Dekking,
Intersections of homogeneous Cantor sets and beta-expansions, Nonlinearity, 23 (2010), 2815-2834.
doi: 10.1088/0951-7715/23/11/005. |
| [18] |
D. Lind and B. Marcus, An Introduction to Symbolic Dynamics and Coding, Cambridge University Press, Cambridge, 1995.
doi: 10.1017/CBO9780511626302.
|
| [19] |
W. Parry,
On the $\beta$-expansions of real numbers, Acta Math. Acad. Sci. Hungar., 11 (1960), 401-416.
doi: 10.1007/BF02020954. |
| [20] |
A. Rényi,
Representations for real numbers and their ergodic properties, Acta Math. Acad. Sci. Hungar., 8 (1957), 477-493.
doi: 10.1007/BF02020331. |
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