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1‐Rotational Steiner triple systems over arbitrary groups
Author(s) -
Buratti Marco
Publication year - 2001
Publication title -
journal of combinatorial designs
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.618
H-Index - 34
eISSN - 1520-6610
pISSN - 1063-8539
DOI - 10.1002/jcd.1008
Subject(s) - mathematics , combinatorics , isomorphism (crystallography) , automorphism , steiner system , abelian group , group (periodic table) , dimension (graph theory) , fixed point , automorphism group , discrete mathematics , crystallography , mathematical analysis , physics , quantum mechanics , chemistry , crystal structure
Phelps and Rosa introduced the concept of 1‐rotational Steiner triple system, that is an STS(ν) admitting an automorphism consisting of a fixed point and a single cycle of length ν − 1 [Discrete Math. 33 (1981), 57–66]. They proved that such an STS(ν) exists if and only if ν ≡ 3 or 9 (mod 24). Here, we speak of a 1‐rotational STS(ν) in a more general sense. An STS(ν) is 1‐rotational over a group G when it admits G as an automorphism group, fixing one point and acting regularly on the other points. Thus the STS(ν)'s by Phelps and Rosa are 1‐rotational over the cyclic group. We denote by 1r , 1r , 1r , 1r , the spectrum of values of ν for which there exists a 1‐rotational STS(ν) over an abelian, a cyclic, a dicyclic, and an arbitrary group, respectively. In this paper, we determine 1r and find partial answers about 1r and 1r . The smallest 1‐rotational STSs have orders 9, 19, 25 and are unique up to isomorphism. In particular, the only 1‐rotational STS(25) is over SL 2 (3), the special linear group of dimension 2 over Z 3 . © 2001 John Wiley & Sons, Inc. J Combin Designs 9: 215–226, 2001