The commuting graph of the symmetric inverse semigroup

Araújo, João; Bentz, Wolfram; Janusz, Konieczny

Abstract

The commuting graph of a finite non-commutative semigroup S, denoted G(S), is a simple graph whose vertices are the non-central elements of S and two distinct vertices x, y are adjacent if xy = yx. Let I(X) be the symmetric inverse semigroup of partial injective transformations on a finite set X. The semigroup I(X) has the symmetric group Sym(X) of permutations on X as its group of units. In 1989, Burns and Goldsmith determined the clique number of the commuting graph of Sym(X). In 2008, Iranmanesh and Jafarzadeh found an upper bound of the diameter of G(Sym(X)), and in 2011, Dolžan and Oblak claimed that this upper bound is in fact the exact value.

The goal of this paper is to begin the study of the commuting graph of the symmetric inverse semigroup I(X). We calculate the clique number of G(I(X)), the diameters of the commuting graphs of the proper ideals of I(X), and the diameter of G(I(X)) when |X| is even or a power of an odd prime. We show that when |X| is odd and divisible by at least two primes, then the diameter of G(I(X)) is either 4 or 5. In the process, we obtain several results about semigroups, such as a description of all commutative subsemigroups of I(X) of maximum order, and analogous results for commutative inverse and commutative nilpotent subsemigroups of I(X). The paper closes with a number of problems for experts in combinatorics and in group or semigroup theory.

Citation

Araújo, J., Bentz, W., & Janusz, K. (2015). The commuting graph of the symmetric inverse semigroup. Israel journal of mathematics, 207(1), 103-149. https://doi.org/10.1007/s11856-015-1173-9

• Journal Article Type: Article
• Acceptance Date: Jan 8, 2013
• Online Publication Date: Mar 28, 2015
• Publication Date: Apr 20, 2015
• Deposit Date: Jun 29, 2018
• Journal: Israel Journal of Mathematics
• Print ISSN: 0021-2172
• Publisher: Springer Verlag
• Peer Reviewed: Peer Reviewed
• Volume: 207
• Issue: 1
• Pages: 103-149
• DOI: https://doi.org/10.1007/s11856-015-1173-9
• Keywords: Inverse Semigroup; Regular Semigroup; Commutative Semigroup; Clique Number; Nilpotent Semigroup
• Public URL: https://hull-repository.worktribe.com/output/900703
• Publisher URL: https://link.springer.com/article/10.1007%2Fs11856-015-1173-9