English

Counting symbol switches in synchronizing automata

Formal Languages and Automata Theory 2018-12-12 v1

Abstract

Instead of looking at the lengths of synchronizing words as in \v{C}ern\'y's conjecture, we look at the switch count of such words, that is, we only count the switches from one letter to another. Where the synchronizing words of the \v{C}ern\'y automata Cn\mathcal{C}_n have switch count linear in nn, we wonder whether synchronizing automata exist for which every synchronizing word has quadratic switch count. The answer is positive: we prove that switch count has the same complexity as synchronizing word length. We give some series of synchronizing automata yielding quadratic switch count, the best one reaching 23n2+O(n)\frac{2}{3} n^2 + O(n) as switch count. We investigate all binary automata on at most 9 states and determine the maximal possible switch count. For all 3n93\leq n\leq 9, a strictly higher switch count can be reached by allowing more symbols. This behaviour differs from length, where for every nn, no automata are known with higher synchronization length than Cn\mathcal{C}_n, which has only two symbols. It is not clear if this pattern extends to larger nn. For n12n\geq 12, our best construction only has two symbols.

Keywords

Cite

@article{arxiv.1812.04050,
  title  = {Counting symbol switches in synchronizing automata},
  author = {Henk Don and Hans Zantema},
  journal= {arXiv preprint arXiv:1812.04050},
  year   = {2018}
}

Comments

26 pages

R2 v1 2026-06-23T06:38:06.569Z