有限或无限字$w$的因子复杂度函数$C_w(n)$对每个$n \ge 0$的长度为$n$的$w$的不同因子的数目进行计数。长度为$|w|$的有限字$w$被称为梯形,如果其因子复杂度$C_w(n)$作为$n$的函数的图(对于$0 \leq n \leq |w|$)是规则梯形(也可能是等腰三角形);即,在长度为$r$某个区间上,$C_w(n)$随着每个$n$增加1,则$C_w(n)$在长度为$s$的某个区间上是常数,最后,在相同长度$r$的间隔上,随着每个$n$,$C_w(n)$减1。必须是$C_w(1)=2$(因为有一个长度因子$0$,即空字),所以任何梯形字都是二进制字母表。梯形词首先由de Luca(1999)在研究有限Sturmian词的因子复杂度的行为时引入,即,因子的无限"切割序列",通过编码序列的削减在一个整数格的正象限的$\mathbb{R}^2$由一条线的无理斜率。每个有限的Sturmian词都是梯形的,但不是相反。然而,这两个词族(梯形和Sturmian)都是所谓的“丰富词”(也称为“完整词”)的特殊类别-一个更广泛的有限和无限词族,其特征是包含最大数量的回文-由第一作者和其他人在2009年深入研究。在本文中,我们介绍了一个自然推广的梯形字在任意有限的字母表$\mathcal{A}$,称为广义梯形字(或GT字简称)。特别是,我们研究了这一类新的词的组合和结构特性,我们表明,与二进制的情况下,并不是所有的GT-词是丰富的回文时,$|\mathcal{A}| \geq 3$,但我们可以描述所有那些丰富的。
英文摘要:
The factor complexity function $C_w(n)$ of a finite or infinite word $w$ counts the number of distinct factors of $w$ of length $n$ for each $n \ge 0$. A finite word $w$ of length $|w|$ is said to be trapezoidal if the graph of its factor complexity $C_w(n)$ as a function of $n$ (for $0 \leq n \leq |w|$) is that of a regular trapezoid (or possibly an isosceles triangle); that is, $C_w(n)$ increases by 1 with each $n$ on some interval of length $r$, then $C_w(n)$ is constant on some interval of length $s$, and finally $C_w(n)$ decreases by 1 with each $n$ on an interval of the same length $r$. Necessarily $C_w(1)=2$ (since there is one factor of length $0$, namely the empty word), so any trapezoidal word is on a binary alphabet. Trapezoidal words were first introduced by de Luca (1999) when studying the behaviour of the factor complexity of finite Sturmian words, i.e., factors of infinite "cutting sequences", obtained by coding the sequence of cuts in an integer lattice over the positive quadrant of $\mathbb{R}^2$ made by a line of irrational slope. Every finite Sturmian word is trapezoidal, but not conversely. However, both families of words (trapezoidal and Sturmian) are special classes of so-called "rich words" (also known as "full words") - a wider family of finite and infinite words characterized by containing the maximal number of palindromes - studied in depth by the first author and others in 2009.
In this paper, we introduce a natural generalization of trapezoidal words over an arbitrary finite alphabet $\mathcal{A}$, called generalized trapezoidal words (or GT-words for short). In particular, we study combinatorial and structural properties of this new class of words, and we show that, unlike the binary case, not all GT-words are rich in palindromes when $|\mathcal{A}| \geq 3$, but we can describe all those that are rich.
Characteristic Parameters and Special Trapezoidal Words
根据Aldo de Luca等人的早期工作,我们研究了梯形词及其前缀的特征参数$K$和$R$(最短不重复后缀的长度和最短无特殊因子的长度),以及它们的对称形式$H$和$L$。我们认为封闭(即,和非。我们的主要结果特征的权利特殊和严格双特殊梯形的话,所做的德卢卡和Mesquisi Sturmian的话。
Factor frequencies in generalized Thue-Morse words
本文描述了广义Thue-Morse字t_{b,m}的因子频率,定义为b大于1,m大于0的整数,作为态射n_{b,m}从0开始的不动点,由n_{b,m}(k)=k(k+1).(k+b-1),其中k = 0,1,.,m-1,其中字母以m为模表示。我们使用A的结果。Frid,On the frequency of factors in a D0L word,Journal of Automata,Languages and Combinatorics 3(1998),29-41 and the study of generalized Thue-Morse words by S. Starosta,Generalized Thue-Morse words and palindromic richness,arXiv:1104.2476v2 [math.CO].
On Periodicity and Complexity of Generalized Pseudostandard Words
广义伪标准词是由de Luca和De Luca在2006年提出的。与回文闭包和伪回文闭包相比,人们对广义伪回文闭包及其相关的广义伪标准词知之甚少。我们提出了两个新的结果,这些话。第一个是它们周期性的充要条件。第二个结果是A. B. Masse,G.Paquin,H. Tremblay和L. Vuillon,On Generalized Pseudostandal Words over Binary Alphabet(Journal of Int.Sequences,16:Article 13.2.11,2013)估计了二进制广义伪标准字的复杂度,即对于所有足够大的n,C(n)小于或等于4n。
Smooth infinite words over $n$-letter alphabets having same remainder when divided by $n$
Brlek et al.(2008)研究了光滑无限词,并建立了一些关于具有相同奇偶性的2字母字母表的字母频率、递归、反转和互补的结果。本文研究了$n$ -字母表$\{a_1,a_2,...,a_n\}$上的光滑无限词,其中$a_1<a_2<...<a_n$是正整数,且被$n$除后余数相同.并设$a_i=n\cdot q_i+r,\;q_i\in N$为$i=1,2,...,n$,其中$r=0,1,2,...,n-1$ .本文用不同的方法证明了:(1)若$r=0$,则二次可微均匀无限字的字母频率为$1/n$,这表明广义Kolakoski序列的字母频率对二字母偶字母为$1/2$;(3)若$r=0$或$r>0 \text{ and }n$为偶数,则广义Kolakoski字对于循环序的字母表$Σ_n$是一致递归的;(4)三次可微无限字的因子集在任何不同的置换下都不是闭的。Brlek等人的结果只是我们相应结果的特例。
研究了P. Duchon提出的一类斜率为(2 m +1)/2的有理Dyck路,它对应于无因子Dyck字.我们表明,在本文中考虑的斜坡,语言的无因子Dyck字生成的辅助语言,我们检查从代数和组合的角度来看。我们提供了这种语言的格路径描述,并给出了一个显式的计数公式的部分贝尔多项式。作为推论,我们得到了新的无关联因子广义Dyck字的个数公式。