On first-fit coloring of ladder-free posets

  • Authors:
  • H. A. Kierstead;Matt Earl Smith

  • Affiliations:
  • -;-

  • Venue:
  • European Journal of Combinatorics
  • Year:
  • 2013

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Abstract

Bosek and Krawczyk exhibited an on-line algorithm for partitioning an on-line poset of width w into w^1^4^l^g^w chains. They also observed that the problem of on-line chain partitioning of general posets of width w could be reduced to First-Fit chain partitioning of 2w^2+1-ladder-free posets of width w, where an m-ladder is the transitive closure of the union of two incomparable chains x"1@?...@?x"m, y"1@?...@?y"m and the set of comparabilities {x"1@?y"1,...,x"m@?y"m}. Here, we provide a subexponential upper bound (in terms of w with m fixed) for the performance of First-Fit chain partitioning on m-ladder-free posets, as well as an exact quadratic bound when m=2, and an upper bound linear in m when w=2. Using the Bosek-Krawczyk observation, this yields an on-line chain partitioning algorithm with a somewhat improved performance bound. More importantly, the algorithm and the proof of its performance bound are much simpler.