The Inapproximability of Non NP-hard Optimization Problems

  • Authors:
  • Liming Cai;David W. Juedes;Iyad Kanj

  • Affiliations:
  • -;-;-

  • Venue:
  • ISAAC '98 Proceedings of the 9th International Symposium on Algorithms and Computation
  • Year:
  • 1998

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Abstract

The inapproximability of non NP-hard optimization problems is investigated. Based on self-reducibility and approximation preserving reductions, it is shown that problems LOG DOMINATING SET, TOURNAMENT DOMINATING SET and RICH HYPERGRAPH VERTEX COVER cannot be approximated to a constant ratio in polynomial time unless the corresponding NP-hard versions are also approximable in deterministic subexponential time. A direct connection is established between non NP-hard problems and a PCP characterization of NP. Reductions from the PCP characterization show that LOG CLIQUE is not approximable in polynomial time and MAX SPARSE SAT does not have a PTAS under the assumption that SAT cannot be solved in deterministic 2O(log n√n) time and that NP ⊈ DTIME(2o(n)).