Improved randomized results for that interval selection problem

Leah Epstein, Asaf Levin

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

Abstract

Online interval selection is a problem in which intervals arrive one by one, sorted by their left endpoints. Each interval has a length and a non-negative weight associated with it. The goal is to select a non-overlapping set of intervals with maximal total weight and run them to completion. The decision regarding a possible selection of an arriving interval must be done immediately upon its arrival. The interval may be preempted later in favor of selecting an arriving overlapping interval, in which case the weight of the preempted interval is lost. We follow Woeginger [10] and study the same models. The type of instances we consider are C-benevolent instances, where the weight of an interval in a monotonically increasing (convex) function of the length, and D-benevolent instances, where the weight of an interval in a monotonically decreasing function of the length. Some of our results can be extended to the case of unit length intervals with arbitrary costs. We significantly improve the previously known bounds on the performance of online randomized algorithms for the problem, namely, we introduce a new algorithm for the D-benevolent case and for unit intervals, which uses a parameter θ and has competitive ratio of at most θ2 ln θ/(θ-1)2. This value is equal to approximately 2.4554 for θ ≈ 3.513 being the solution of the equation x - 1 = 2ln x. We further design a lower bound of 1 + ln 2 ≈ 1.693 on the competitive ratio of any randomized algorithm. The lower bound is valid for any C-benevolent instance, some D-benevolent functions and for unit intervals. We further show a lower bound of 3/2 for a wider class of D-benevolent instances. This improves over previously known lower bounds. We also design a barely random online algorithm for the D-benevolent case and the case of unit intervals, which uses a single random bit, and has a competitive ratio of 3.22745.

Original languageEnglish
Title of host publicationAlgorithms - ESA 2008 - 16th Annual European Symposium, Proceedings
PublisherSpringer Verlag
Pages381-392
Number of pages12
ISBN (Print)3540877436, 9783540877431
DOIs
StatePublished - 2008
Event16th Annual European Symposium on Algorithms, ESA 2008 - Karlsruhe, Germany
Duration: 15 Sep 200817 Sep 2008

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Volume5193 LNCS
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349

Conference

Conference16th Annual European Symposium on Algorithms, ESA 2008
Country/TerritoryGermany
CityKarlsruhe
Period15/09/0817/09/08

ASJC Scopus subject areas

  • Theoretical Computer Science
  • Computer Science (all)

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