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Augmenting a Submodular and Posi-modular Set Function by a Multigraph
Authors:Hiroshi Nagamochi  Takashi Shiraki  Toshihide Ibaraki
Institution:(1) Department of Information and Computer Sciences, Toyohashi University of Technology, Tempaku, Toyohashi, 441-8580, Japan;(2) 1st Laboratory, Development Laboratories, NEC Networks Abiko, Chiba, 270-1198, Japan;(3) Department of Applied Mathematics and Physics, Kyoto University, Sakyo, Kyoto, 606-8501, Japan
Abstract:Given a finite set V and a set function 
$$f:2^V \mapsto Z$$
, we consider the problem of constructing an undirected multigraph G = (V,E) such that the cut function 
$$C_G :2^V \mapsto Z{\text{ of }}G{\text{ and }}f$$
together has value at least 2 for all non-empty and proper subsets of V. If f is intersecting submodular and posi-modular, and satisfies the tripartite inequality, then we show that such a multigraph G with the minimum number of edges can be found in 
$$O\left( {\left( {T_f + 1} \right)n^4 \log n} \right)$$
time, where 
$$n = \left| V \right|{\text{ and }}T_f$$
is the time to compute the value of f(X) for a subset 
$$X \subset V$$
.
Keywords:algorithms  submodular function  posi-modular function  minimum cut  edge-connectivity  undirected graph  edge-splitting  graph augmentation
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