
handle: 11245/1.153357
Let \(G=(V,E)\) be an undirected graph and \(\{S,T\}\) a partition of \(V\). Then a set of edges \(F\subseteq E\) such that every component of the subgraph \((V,F)\) intersects both \(S\) and \(T\), is called an \(S\)--\(T\) connector. In general a subpartition \(W\) of a set \(X\) is a collection of pairwise disjoint nonempty subsets of \(X\); and if---like in the present case---\(W=\{U_1, \dots, U_t\}\) is a subpartition of \(S\) or \(T\), then \(\delta(W)\) denotes the set of edges with one end in \(U_i\) and one end in \(V\setminus U_i\) for some index \(i\). The main result of this paper is Theorem 1: \(G\) contains \(k\) edge-disjoint \(S\)--\(T\) connectors iff \(|\delta (W)|\geq k\cdot | W|\) for every subpartition \(W\) of \(S\) or \(T\), where \(k\) is a natural number. This result is a generalization of a theorem on (i) disjoint edge covers in a bipartite graph (König/Gupta), and (ii) disjoint spanning trees in an undirected graph (Tutte/Nash-Williams), stated here as Lemma 1. According to the concept of \(S\)--\(T\) connector in undirected graphs the \(S\)--\(T\) bibranching is defined in directed graphs and a result of Schrijver with respect to packing bibranches is given as Lemma 2. The proof of Theorem 1 follows essentially by combining both these lemmas. Simultaneously this proof yields the basis for a polynomial algorithm for packing \(S\)--\(T\) connectors not described in the present paper. Finally, in Section 3, it is shown that Theorem 1 implies the integer rounding property for a set of linear inequalities associated with packing \(S\)--\(T\) connectors. The polyhedral formulation of this fact is given in Theorem 2.
Computational Theory and Mathematics, Edge subsets with special properties (factorization, matching, partitioning, covering and packing, etc.), Discrete Mathematics and Combinatorics, connector, Structural characterization of families of graphs, partition, Trees, packing bibranches, Theoretical Computer Science
Computational Theory and Mathematics, Edge subsets with special properties (factorization, matching, partitioning, covering and packing, etc.), Discrete Mathematics and Combinatorics, connector, Structural characterization of families of graphs, partition, Trees, packing bibranches, Theoretical Computer Science
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