Structural aspects of semigroups based on digraphs

East, James; Gadouleau, Maximilien; Mitchell, James D.

doi:10.5802/alco.56

East, James; Gadouleau, Maximilien; Mitchell, James D.

Algebraic Combinatorics, Volume 2 (2019) no. 5, p. 711-733

Abstract

Given any digraph $D$ without loops or multiple arcs, there is a natural construction of a semigroup $〈 D 〉$ of transformations. To every arc $(a, b)$ of $D$ is associated the idempotent transformation $(a \to b)$ mapping $a$ to $b$ and fixing all vertices other than $a$ . The semigroup $〈 D 〉$ is generated by the idempotent transformations $(a \to b)$ for all arcs $(a, b)$ of $D$ .

In this paper, we consider the question of when there is a transformation in $〈 D 〉$ containing a large cycle, and, for fixed $k \in ℕ$ , we give a linear time algorithm to verify if $〈 D 〉$ contains a transformation with a cycle of length $k$ . We also classify those digraphs $D$ such that $〈 D 〉$ has one of the following properties: inverse, completely regular, commutative, simple, 0-simple, a semilattice, a rectangular band, congruence-free, is $𝒦$ -trivial or $𝒦$ -universal where $𝒦$ is any of Green’s $ℋ$ -, $ℒ$ -, $ℛ$ -, or $𝒥$ -relation, and when $〈 D 〉$ has a left, right, or two-sided zero.

Received : 2018-03-02
Revised : 2018-11-26
Accepted : 2018-12-21
Published online : 2019-10-08
DOI : https://doi.org/10.5802/alco.56
Classification: 20M20, 05C20, 05C25
Keywords: digraphs, flow semigroup of digraph, semigroups, monoids

@article{ALCO_2019__2_5_711_0,
     author = {East, James and Gadouleau, Maximilien and Mitchell, James D.},
     title = {Structural aspects of semigroups based on digraphs},
     journal = {Algebraic Combinatorics},
     publisher = {MathOA foundation},
     volume = {2},
     number = {5},
     year = {2019},
     pages = {711-733},
     doi = {10.5802/alco.56},
     language = {en},
     url = {https://alco.centre-mersenne.org/item/ALCO_2019__2_5_711_0}
}

East, James; Gadouleau, Maximilien; Mitchell, James D. Structural aspects of semigroups based on digraphs. Algebraic Combinatorics, Volume 2 (2019) no. 5, pp. 711-733. doi : 10.5802/alco.56. https://alco.centre-mersenne.org/item/ALCO_2019__2_5_711_0/

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