Approximating infeasible 2VPI-systems

  • Authors:
  • Neele Leithäuser;Sven O. Krumke;Maximilian Merkert

  • Affiliations:
  • ITWM Fraunhofer Institut für Techno- und Wirtschaftsmathematik, Kaiserslautern, Germany;Dept. of Mathematics, University of Kaiserslautern, Kaiserslautern, Germany;Dept. of Mathematics, University of Kaiserslautern, Kaiserslautern, Germany

  • Venue:
  • WG'12 Proceedings of the 38th international conference on Graph-Theoretic Concepts in Computer Science
  • Year:
  • 2012

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Abstract

It is a folklore result that testing whether a given system of equations with two variables per inequality (a 2VPI system) of the form xi−xj=cij is solvable, can be done efficiently not only by Gaussian elimination but also by shortest-path computation on an associated constraint graph. However, when the system is infeasible and one wishes to delete a minimum weight set of inequalities to obtain feasibility (MinFs2=), this task becomes NP-complete. Our main result is a 2-approximation for the problem MinFs2= for the case when the constraint graph is planar using a primal-dual approach. We also give an α-approximation for the related maximization problem MaxFs2= where the goal is to maximize the weight of feasible inequalities. Here, α denotes the arboricity of the constraint graph. Our results extend to obtain constant factor approximations for the case when the domains of the variables are further restricted.