DMGT

ISSN 1234-3099 (print version)

ISSN 2083-5892 (electronic version)

https://doi.org/10.7151/dmgt

Discussiones Mathematicae Graph Theory

Journal Impact Factor (JIF 2023): 0.5

5-year Journal Impact Factor (2023): 0.6

CiteScore (2023): 2.2

SNIP (2023): 0.681

Discussiones Mathematicae Graph Theory

Article in press


Authors:

J. Morris

Joy Morris

Department of Mathematics and Computer Science
University of Lethbridge
Lethbridge, AB T1K 3M4

email: joy.morris@uleth.ca

0000 0003 2416 669X

Title:

Walecki tournaments with an arc that lies in a unique directed triangle

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Source:

Discussiones Mathematicae Graph Theory

Received: 2024-08-19 , Revised: 2024-12-07 , Accepted: 2024-12-09 , Available online: 2025-01-10 , https://doi.org/10.7151/dmgt.2573

Abstract:

A Walecki tournament is any tournament that can be formed by choosing an orientation for each of the Hamilton cycles in the Walecki decomposition of a complete graph on an odd number of vertices. In this paper, we show that if some arc in a Walecki tournament on at least $7$ vertices lies in exactly one directed triangle, then there is a vertex of the tournament (the vertex typically labelled $*$ in the decomposition) that is fixed under every automorphism of the tournament. Furthermore, any isomorphism between such Walecki tournaments maps the vertex labelled $*$ in one to the vertex labelled $*$ in the other. We also show that among Walecki tournaments with a signature of even length $2k$, of the $2^{2k}$ possible signatures, at least $2^k$ produce tournaments that have an arc that lies in a unique directed triangle (and therefore to which our result applies).

Keywords:

tournaments, Walecki decomposition, Walecki tournaments, automorphisms, isomorphisms

References:

  1. J. Aleš, Automorphism Groups of Walecki Tournaments, Ph.D Thesis (Simon Fraser University, Burnaby, 1999).
  2. J. Aleš, Automorphism groups of Walecki tournaments with zero and odd signatures, Art Discrete Appl. Math. 2 (2018) #P1.06.
    https://doi.org/10.26493/2590-9770.1266.729
  3. B. Alspach, A Class of Tournaments, Ph.D Thesis (University of California, Santa Barbara, 1966).
  4. B. Alspach, K.B. Reid and D.P. Roselle, Bypasses in asymmetric digraphs, J. Combin. Theory Ser. B 17 (1974) 11–18.
    https://doi.org/10.1016/0095-8956(74)90041-0

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