Mixed-Integer Vertex Covers on Bipartite Graphs

  • Authors:
  • Michele Conforti;Bert Gerards;Giacomo Zambelli

  • Affiliations:
  • Dipartimento di Matematica Pura e Applicata, Universitá di Padova, Via Trieste 63, 35121 Padova, Italy;Centrum voor Wiskunde en Informatica, Kruislaan 413, 1098 SJ Amsterdam, The Netherlands and Technische Universiteit Eindhoven, Den Dolech 2, Eindhoven, The Netherlands;Dipartimento di Matematica Pura e Applicata, Universitá di Padova, Via Trieste 63, 35121 Padova, Italy

  • Venue:
  • IPCO '07 Proceedings of the 12th international conference on Integer Programming and Combinatorial Optimization
  • Year:
  • 2007

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Abstract

Let Abe the edge-node incidence matrix of a bipartite graph G= (U,V;E), Ibe a subset of the nodes of G, and bbe a vector such that 2bis integral. We consider the following mixed-integer set:$$X(G,b,I)=\{x\,:\,Ax\geq b,\,x\geq 0,\,x_i\mbox{ integer for all }i\in I\}.$$We characterize conv(X(G,b,I)) in its original space. That is, we describe a matrix (C,d) such that conv(X(G,b,I)) = {x: Cx茂戮驴 d}. This is accomplished by computing the projection onto the space of the x-variables of an extended formulation, given in [1], for conv(X(G,b,I)). We then give a polynomial-time algorithm for the separation problem for conv(X(G,b,I)), thus showing that the problem of optimizing a linear function over the set X(G,b,I) is solvable in polynomial time.