Characterization of removable elements with respect to having k disjoint bases in a matroid

  • Authors:
  • Ping Li;Hong-Jian Lai;Yanting Liang

  • Affiliations:
  • Department of Mathematics, Beijing Jiaotong University, Beijing 100044, PR China;College of Mathematics and System Sciences, Xinjiang University, Urumqi, Xinjiang 830046, PR China and Department of Mathematics, West Virginia University, Morgantown, WV 26506, USA;Department of Mathematics, University of Wisconsin-Fond du Lac, Fond du Lac, WI 54935, USA

  • Venue:
  • Discrete Applied Mathematics
  • Year:
  • 2012

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Abstract

The well-known spanning tree packing theorem of Nash-Williams and Tutte characterizes graphs with k edge-disjoint spanning trees. Edmonds generalizes this theorem to matroids with k disjoint bases. For any graph G that may not have k-edge-disjoint spanning trees, the problem of determining what edges should be added to G so that the resulting graph has k edge-disjoint spanning trees has been studied by Haas (2002) [11] and Liu et al. (2009) [17], among others. This paper aims to determine, for a matroid M that has k disjoint bases, the set E"k(M) of elements in M such that for any e@?E"k(M), M-e also has k disjoint bases. Using the matroid strength defined by Catlin et al. (1992) [4], we present a characterization of E"k(M) in terms of the strength of M. Consequently, this yields a characterization of edge sets E"k(G) in a graph G with at least k edge-disjoint spanning trees such that @?e@?E"k(G), G-e also has k edge-disjoint spanning trees. Polynomial algorithms are also discussed for identifying the set E"k(M) in a matroid M, or the edge subset E"k(G) for a connected graph G.