Directed strongly regular graphs obtained from coherent algebras

Mikhail Klin, Akihiro Munemasa, Mikhail Muzychuk, Paul Hermann Zieschang

Research output: Contribution to journalArticlepeer-review

30 Citations (Scopus)

Abstract

The notion of a directed strongly regular graph was introduced by A. Duval in 1988 as one of the possible generalizations of classical strongly regular graphs to the directed case. We investigate this generalization with the aid of coherent algebras in the sense of D.G. Higman. We show that the coherent algebra of a mixed directed strongly regular graph is a non-commutative algebra of rank at least 6. With this in mind, we examine the group algebras of dihedral groups, the flag algebras of a Steiner 2-designs, in search of directed strongly regular graphs. As a result, a few new infinite series of directed strongly regular graphs are constructed. In particular, this provides a positive answer to a question of Duval on the existence of a graph with certain parameter set having 20 vertices. One more open case with 14 vertices listed in Duval's paper is ruled out, while new interpretations in terms of coherent algebras are given for many of Duval's results.

Original languageEnglish
Pages (from-to)83-109
Number of pages27
JournalLinear Algebra and Its Applications
Volume377
Issue number1-3
DOIs
Publication statusPublished - 2004 Jan 15

Keywords

  • Automorphism group
  • Building
  • Coherent algebra
  • Dihedral group
  • Directed strongly regular graph
  • Doubly regular tournament
  • Flag algebra
  • Permutation group
  • Steiner system

ASJC Scopus subject areas

  • Algebra and Number Theory
  • Numerical Analysis
  • Geometry and Topology
  • Discrete Mathematics and Combinatorics

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