Recognizing Bipartite Incident-Graphs of Circulant Digraphs

  • Authors:
  • Johanne Cohen;Pierre Fraigniaud;Cyril Gavoille

  • Affiliations:
  • -;-;-

  • Venue:
  • WG '99 Proceedings of the 25th International Workshop on Graph-Theoretic Concepts in Computer Science
  • Year:
  • 1999

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Abstract

Knödel graphs and Fibonacci graphs are two classes of bipartite incident-graph of circulant digraphs. Both graphs have been extensively studied for the purpose of fast communications in networks, and they have deserved a lot of attention in this context. In this paper, we show that there exists an O(n log5 n)-time algorithm to recognize Knödel graphs, and that the same technique applies to Fibonacci graphs. The algorithm is based on a characterization of the cycles of length six in these graphs (bipartite incident-graphs of circulant digraphs always have cycles of length six). A consequence of our result is that none of the Knödel graphs are edge-transitive, apart those of 2k -2 vertices. An open problem that arises in this field is to derive a polynomial-time algorithm for any infinite family of bipartite incident-graphs of circulant digraphs indexed by their number of vertices.