Approximation hardness of deadline-TSP reoptimization

  • Authors:
  • Hans-Joachim Böckenhauer;Joachim Kneis;Joachim Kupke

  • Affiliations:
  • Department of Computer Science, ETH Zurich, Switzerland;Department of Computer Science, RWTH Aachen University, Germany;Google Inc., Mountain View, USA

  • Venue:
  • Theoretical Computer Science
  • Year:
  • 2009

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Abstract

Given an instance of an optimization problem together with an optimal solution, we consider the scenario in which this instance is modified locally. In graph problems, e.g., a singular edge might be removed or added, or an edge weight might be varied, etc. For a problem U and such a local modification operation, let lm-U (local-modification-U) denote the resulting problem. The question is whether it is possible to exploit the additional knowledge of an optimal solution to the original instance or not, i.e.,whether lm-U is computationally more tractable than U. While positive examples are known e.g. for metric TSP, we give some negative examples here: Metric TSP with deadlines (time windows), if a single deadline or the cost of a single edge is modified, exhibits the same lower bounds on the approximability in these local-modification versions as those currently known for the original problem.