A Characterization of Morphic Words with Polynomial Growth
Discrete mathematics & theoretical computer science, Tome 22 (2020-2021) no. 1
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A morphic word is obtained by iterating a morphism to generate an infinite word, and then applying a coding. We characterize morphic words with polynomial growth in terms of a new type of infinite word called a $\textit{zigzag word}$. A zigzag word is represented by an initial string, followed by a finite list of terms, each of which repeats for each $n \geq 1$ in one of three ways: it grows forward [$t(1)\ t(2)\ \dotsm\ t(n)]$, backward [$t(n)\ \dotsm\ t(2)\ t(1)$], or just occurs once [$t$]. Each term can recursively contain subterms with their own forward and backward repetitions. We show that an infinite word is morphic with growth $\Theta(n^k)$ iff it is a zigzag word of depth $k$. As corollaries, we obtain that the morphic words with growth $O(n)$ are exactly the ultimately periodic words, and the morphic words with growth $O(n^2)$ are exactly the multilinear words.
@article{DMTCS_2020_22_1_a3,
author = {Smith, Tim},
title = {A {Characterization} of {Morphic} {Words} with {Polynomial} {Growth}},
journal = {Discrete mathematics & theoretical computer science},
year = {2020-2021},
volume = {22},
number = {1},
doi = {10.23638/DMTCS-22-1-3},
language = {en},
url = {http://geodesic.mathdoc.fr/articles/10.23638/DMTCS-22-1-3/}
}
TY - JOUR AU - Smith, Tim TI - A Characterization of Morphic Words with Polynomial Growth JO - Discrete mathematics & theoretical computer science PY - 2020-2021 VL - 22 IS - 1 UR - http://geodesic.mathdoc.fr/articles/10.23638/DMTCS-22-1-3/ DO - 10.23638/DMTCS-22-1-3 LA - en ID - DMTCS_2020_22_1_a3 ER -
Smith, Tim. A Characterization of Morphic Words with Polynomial Growth. Discrete mathematics & theoretical computer science, Tome 22 (2020-2021) no. 1. doi: 10.23638/DMTCS-22-1-3
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