Excessive factorizations of bipartite multigraphs

  • Authors:
  • David Cariolaro;Romeo Rizzi

  • Affiliations:
  • Department of Mathematical Sciences, Xi'an Jiaotong-Liverpool University, Suzhou, Jiangsu 215213, China;Dipartimento di Matematica ed Informatica, Universití di Udine, Italy

  • Venue:
  • Discrete Applied Mathematics
  • Year:
  • 2010

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Abstract

An excessive factorization of a multigraph G is a set F={F"1,F"2,...,F"r} of 1-factors of G whose union is E(G) and, subject to this condition, r is minimum. The integer r is called the excessive index of G and denoted by @g"e^'(G). We set @g"e^'(G)=~ if an excessive factorization does not exist. Analogously, let m be a fixed positive integer. An excessive[m]-factorization is a set M={M"1,M"2,...,M"k} of matchings of G, all of size m, whose union is E(G) and, subject to this condition, k is minimum. The integer k is denoted by @g"["m"]^'(G) and called the excessive [m]-index of G. Again, we set @g"["m"]^'(G)=~ if an excessive [m]-factorization does not exist. In this paper we shall prove that, for bipartite multigraphs, both the parameters @g"e^' and @g"["m"]^' are computable in polynomial time, and we shall obtain an efficient algorithm for finding an excessive factorization and excessive [m]-factorization, respectively, of any bipartite multigraph.