Imprimitive cometric association schemes: Constructions and analysis

  • Authors:
  • William J. Martin;Mikhail Muzychuk;Jason Williford

  • Affiliations:
  • Department of Mathematical Sciences and Department of Computer Science, Worcester Polytechnic Institute, Worcester, USA;Department of Computer Science and Mathematics, Netanya Academic College, Netanya, Israel 42365;Department of Mathematical Sciences, Worcester Polytechnic Institute, Worcester, USA

  • Venue:
  • Journal of Algebraic Combinatorics: An International Journal
  • Year:
  • 2007

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Abstract

Dualizing the "extended bipartite double" construction for distance-regular graphs, we construct a new family of cometric (or Q-polynomial) association schemes with four associate classes based on linked systems of symmetric designs. The analysis of these new schemes naturally leads to structural questions concerning imprimitive cometric association schemes, some of which we answer with others being left as open problems. In particular, we prove that any Q-antipodal association scheme is dismantlable: the configuration induced on any subset of the equivalence classes in the Q-antipodal imprimitivity system is again a cometric association scheme. Further examples are explored.