Discrete Mathematics & Theoretical Computer Science |

- 1 Algorithmics Research Group

We analyze on-line chain partitioning problem and its variants as a two-person game. One person (Spoiler) builds an on-line poset presenting one point at time. The other one (Algorithm) assigns new point to a chain. Kierstead gave a strategy for Algorithm showing that width w posets can be on-line chain partitioned into $\frac{{5}^{w-1}}{4}$ chains. Felsner proved that if Spoiler presents an upgrowing poset, i.e., each new point is maximal at the moment of its arrival then there is a strategy for Algorithm using at most $\binom{w+1}{2}$ chains and it is best possible. An adaptive variant of this problem allows Algorithm to assign to the new point a set of chains and than to remove some of them (but not all) while covering next points. Felsner stated a hypothesis that in on-line adaptive chain covering of upgrowing posets Algorithm may use smaller number of chains than in non-adaptive version. In this paper we provide an argument suggesting that it is true. We present a class of upgrowing posets in which Spoiler has a strategy forcing Algorithm to use at least $\binom{w+1}{2}$ chains (in non-adaptive version) and Algorithm has a strategy using at most $O(w\sqrt{w})$ chains in adaptive version.

Source: HAL:hal-01183337v1

Volume: DMTCS Proceedings vol. AF, Computational Logic and Applications (CLA '05)

Section: Proceedings

Published on: January 1, 2005

Imported on: May 10, 2017

Keywords: poset,order,on-line algorithm,chain partition,[INFO.INFO-LO] Computer Science [cs]/Logic in Computer Science [cs.LO],[INFO.INFO-SC] Computer Science [cs]/Symbolic Computation [cs.SC],[INFO.INFO-HC] Computer Science [cs]/Human-Computer Interaction [cs.HC]

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