On the capacity of information networks
SODA '06 Proceedings of the seventeenth annual ACM-SIAM symposium on Discrete algorithm
Hardness of cut problems in directed graphs
Proceedings of the thirty-eighth annual ACM symposium on Theory of computing
An O(√n)-approximation algorithm for directed sparsest cut
Information Processing Letters
On the max-flow min-cut ratio for directed multicommodity flows
Theoretical Computer Science
Polynomial flow-cut gaps and hardness of directed cut problems
Proceedings of the thirty-ninth annual ACM symposium on Theory of computing
Improved approximation for directed cut problems
Proceedings of the thirty-ninth annual ACM symposium on Theory of computing
Polynomial flow-cut gaps and hardness of directed cut problems
Journal of the ACM (JACM)
An O(n)-approximation algorithm for directed sparsest cut
Information Processing Letters
The Brunn-Minkowski Inequality and Nontrivial Cycles in the Discrete Torus
SIAM Journal on Discrete Mathematics
Multicommodity flows and cuts in polymatroidal networks
Proceedings of the 3rd Innovations in Theoretical Computer Science Conference
Eliminating cycles in the discrete torus
LATIN'06 Proceedings of the 7th Latin American conference on Theoretical Informatics
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Given a directed edge-weighted graph and k source-sink pairs, the Minimum Directed Multicut Problem is to find an edge subset with minimal weight, that separates each source-sink pair. Determining the minimum multicut in directed or undirected graphs is NP-hard. The fractional version of the minimum multicut problem is dual to the maximum multicommodity flow problem. The integrality gap for an instance of this problem is the ratio of the minimum weight multicut to the minimum weight fractional multicut; trivially this gap is always at least 1 and it is easy to show that it is at most k. In the analogous problem for undirected graphs this upper bound was improved to O(log k).In this paper, for each k an explicit family of examples is presented each with k source-sink pairs for which the integrality gap can be made arbitrarily close to k. This shows that for directed graphs, the trivial upper bound of k can not be improved.