Some problems on factorizations with constraints in bipartite graphs

  • Authors:
  • Guizhen Liu;Binhai Zhu

  • Affiliations:
  • Department of Mathematics, Shandong University at Weihai, Shandong 264209, People's Republic of China;Department of Computer Science, Montana State University, Bozeman MT

  • Venue:
  • Discrete Applied Mathematics
  • Year:
  • 2003

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Abstract

Let G = (X, Y, E(G)) be a bipartite graph with vertex set V(G) = X ∪ Y and edge set E(G) and let g and f be two non-negative integer-valued functions defined on V(G) such that g(x) ≤ f(x) for each x ∈ V(G). A (g, f)-factor of G is a spanning subgraph F of G such that g(x) ≤ dF(x) ≤ f(x) for each x ∈ V(F); a (g, f)-factorization of G is a partition of E(G) into edge-disjoint (g, f)-factors. In this paper it is proved that every bipartite (mg + m - 1, mf - m + 1)-graph has (g, f)-factorizations randomly k-orthogonal to any given subgraph with km edges if k ≤ g(x) for any x ∈ V(G) and has a (g, f)-factorization k-orthogonal to any given subgraph with km edges if k - 1 ≤ g(x) for any x ∈ V(G) and that every bipartite (mg, m f)-graph has a (g, f)-factorization orthogonal to any given m-star if 0 ≤ g(x) ≤ f(x) for any x ∈ V(G). Furthermore, it is shown that there are polynomial algorithms for finding the desired factorizations and the results in this paper are in some sense best possible.