Matching graphs of hypercubes and complete bipartite graphs

  • Authors:
  • Jiří Fink

  • Affiliations:
  • Department of Applied Mathematics, Faculty of Mathematics and Physics, Charles University, Malostranské námstí 25, 118 00 Prague 1, Czech Republic

  • Venue:
  • European Journal of Combinatorics
  • Year:
  • 2009

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Abstract

Kreweras' conjecture [G. Kreweras, Matchings and hamiltonian cycles on hypercubes, Bull. Inst. Combin. Appl. 16 (1996) 87-91] asserts that every perfect matching of the hypercube Q"d can be extended to a Hamiltonian cycle of Q"d. We [Jiri Fink, Perfect matchings extend to hamilton cycles in hypercubes, J. Combin. Theory Ser. B, 97 (6) (2007) 1074-1076] proved this conjecture but here we present a simplified proof. The matching graphM(G) of a graph G has a vertex set of all perfect matchings of G, with two vertices being adjacent whenever the union of the corresponding perfect matchings forms a Hamiltonian cycle of G. We show that the matching graph M(K"n","n) of a complete bipartite graph is bipartite if and only if n is even or n=1. We prove that M(K"n","n) is connected for n even and M(K"n","n) has two components for n odd, n=3. We also compute distances between perfect matchings in M(K"n","n).