A matroid approach to finding edge connectivity and packing arborescences
Selected papers of the 23rd annual ACM symposium on Theory of computing
AAIM '07 Proceedings of the 3rd international conference on Algorithmic Aspects in Information and Management
Covering Directed Graphs by In-Trees
COCOON '08 Proceedings of the 14th annual international conference on Computing and Combinatorics
Discrete Applied Mathematics
Covering directed graphs by in-trees
Journal of Combinatorial Optimization
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Given a directed graph D = (V, A) and a set of specified vertices S = {s1,…,sd} ⊆ V with |S| = d and a function f: S → N where N denotes the set of natural numbers, we present a necessary and sufficient condition that there exist Σsi ε arc-disjoint in-trees denoted by Ti,1,Ti,2,…,Tif (si) for every i = 1,…,d such that Ti,1,…, Ti,f(si) are rooted at si and each Ti,j spans vertices from which si is reachable. This generalizes the result of Edmonds [2], i.e., the necessary and sufficient condition that for a directed graph D = (V,A) with a specified vertex s ε V, there are k arc-disjoint in-trees rooted at s each of which spans V. Furthermore, we extend another characterization of packing in-trees of Edmonds [1] to the one in our case.