A Note on A Family of Directed Strongly Regular Graphs

نویسندگان

  • Sylvia A. Hobart
  • T. Justin Shaw
چکیده

where J is the all ones matrix and I is the identity. These matrix conditions are equivalent to the combinatorial conditions that the graph is both inand out-regular, and that the number of directed 2-paths from a vertex x to a vertex y is t if x = y, λ if x → y, and μ otherwise. Recently, these graphs were studied by Klin et al. [2], including some new constructions and a list of feasible parameters. In this note, we will use Cayley graphs to construct a new infinite family of dsrg’s. For any subset S of a group G, the (directed) Cayley graph of G with respect to S, denoted C(G, S), is the directed graph with vertex set G where g→ h if and only if hg−1 ∈ S. We can determine whether a Cayley graph is a dsrg using the group ring ZG. For any subset T ⊆ G, define T ∈ ZG by T = ∑ t∈T t . LEMMA 1. The Cayley graph C(G, S), is a (v, k, μ, λ, t)-dsrg if and only if the equation S 2 = te + λS + μ(G − e − S) holds in ZG.

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عنوان ژورنال:
  • Eur. J. Comb.

دوره 20  شماره 

صفحات  -

تاریخ انتشار 1999