Fitting Points on the Real Line and Its Application to RH Mapping

  • Authors:
  • Johan Håstad;Lars Ivansson;Jens Lagergren

  • Affiliations:
  • -;-;-

  • Venue:
  • ESA '98 Proceedings of the 6th Annual European Symposium on Algorithms
  • Year:
  • 1998

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Abstract

The MATRIX-TO-LINE problem is that of, given an n × n symmetric matrix D, finding an arrangement of n points on the real line such that the so obtained distances agree as well as possible with the by D specified distances, w.r.t. the max-norm. The MATRIX-TO-LINE problem has previously been shown to be NP-complete [11]. We show that it can be approximated within 2, but not within 4=3 unless P=NP. We also show tight bounds under a stronger assumption. We show that the MATRIX-TO-LINE problem cannot be approximated within 2 - δ unless 3-colorable graphs can be colored with ⌊4/δ⌋ colors in polynomial time. Currently, the best polynomial time algorithm colors a 3-colorable graph with Õ(n3/14) colors [4]. We apply our MATRIX-TO-LINE algorithm to a problem in computational biology, namely, the Radiation Hybrid (RH) problem, i.e., the algorithmic part of a physical mapping method called RH mapping. This gives us the first algorithm with a guaranteed convergence for the general RH problem.