Testing branch-width

  • Authors:
  • Sang-il Oum;Paul Seymour

  • Affiliations:
  • School of Mathematics, Georgia Institute of Technology, Atlanta, GA, USA;Department of Mathematics, Princeton University, Princeton, NJ, USA

  • Venue:
  • Journal of Combinatorial Theory Series B
  • Year:
  • 2007

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Abstract

An integer-valued function f on the set 2^V of all subsets of a finite set V is a connectivity function if it satisfies the following conditions: (1) f(X)+f(Y)=f(X@?Y)+f(X@?Y) for all subsets X, Y of V, (2) f(X)=f(V@?X) for all X@?V, and (3) f(@A)=0. Branch-width is defined for graphs, matroids, and more generally, connectivity functions. We show that for each constant k, there is a polynomial-time (in |V|) algorithm to decide whether the branch-width of a connectivity function f is at most k, if f is given by an oracle. This algorithm can be applied to branch-width, carving-width, and rank-width of graphs. In particular, we can recognize matroids M of branch-width at most k in polynomial (in |E(M)|) time if the matroid is given by an independence oracle.