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Maximal pattern complexity for Toeplitz words

Published online by Cambridge University Press:  10 July 2006

NERTILA GJINI
Affiliation:
University of New York, Tirana, Albania (e-mail: ngjini@unyt.edu.al)
TETURO KAMAE
Affiliation:
Matsuyama University, 790-8578 Matsuyama, Japan (e-mail: kamae@apost.plala.or.jp)
TAN BO
Affiliation:
Department of Mathematics, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China (e-mail: bo_tan@163.com)
XUE YU-MEI
Affiliation:
Department of Mathematics, Tsinghua University, Beijing 100084, People's Republic of China (e-mail: yxue@math.tsinghua.edu.cn)

Abstract

The notion of the maximal pattern complexity of words was introduced by Kamae and Zamboni. In this paper, we obtain an almost exact formula for the maximal pattern complexity $p^*_\alpha(k)$ of Toeplitz words $\alpha$ on an alphabet ${\mathbb A}$ defined by a sequence of coding words $(\eta^{(n)})^\infty\in({\mathbb A}\cup\{?\})^{\mathbb N}(n=1,2,\dotsc)$ including just one ‘?’ in their cycles $\eta^{(n)}$. Using this formula, we characterize pattern Sturmian words (i.e. $p^*_\alpha(k)=2k$ (for all $k$)) in this class. Moreover, we give a characterization of simple Toeplitz words in the sense of Kamae and Zamboni in terms of pattern complexity. In the case where $\eta^{(1)}=\eta^{(2)}=\dotsb$, we obtain the value $\lim_{k\to\infty}p_\alpha^*(k)/k$. We construct a Toeplitz word $\alpha\in{\mathbb A}^{\mathbb N}$ with $\#\A=2$ such that $p^*_\alpha(k)=2^k~(k=1,2,\dotsc)$, while Toeplitz words in our sense always have discrete spectra.

Type
Research Article
Copyright
2006 Cambridge University Press

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