Multiroute flows: Cut-trees and realizability

  • Authors:
  • Santosh N. Kabadi;R. Chandrasekaran;K. P. K. Nair

  • Affiliations:
  • Faculty of Business Administration, University of New Brunswick, Fredericton, N.B., Canada E3B5A3;Department of Computer Science, University of Texas at Dallas, Richardson, Texas, USA;Faculty of Business Administration, University of New Brunswick, Fredericton, N.B., Canada E3B5A3

  • Venue:
  • Discrete Optimization
  • Year:
  • 2005

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Abstract

In the context of q-route flows in an undirected network with non-negative edge capacities, for integer values of q=2, we consider two problems of both theoretical and practical interest. The first problem focuses on investigating the existence and construction of a cut-tree. For q=2, we show that a cut-tree always exists and can be constructed in strongly polynomial time. However, for q=3, in general, a cut-tree does not exist and we establish this through a counter-example. The second problem addresses the issue of checking if a given matrix R is 2-realizable-that is, checking if there exists an undirected, simple network with non-negative edge capacities such that the non-diagonal elements of R are precisely the maximum 2-route flow values between corresponding pairs of nodes in the network. We provide a complete characterization of 2-realizable matrices and using this characterization, we prove that the problem of testing if a given matrix is 2-realizable is, in general, NP-complete.