Approximation algorithms for online weighted rank function maximization under matroid constraints

Niv Buchbinder, Joseph Naor, R. Ravi, Mohit Singh

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


Consider the following online version of the submodular maximization problem under a matroid constraint. We are given a set of elements over which a matroid is defined. The goal is to incrementally choose a subset that remains independent in the matroid over time. At each time, a new weighted rank function of a different matroid (one per time) over the same elements is presented; the algorithm can add a few elements to the incrementally constructed set, and reaps a reward equal to the value of the new weighted rank function on the current set. The goal of the algorithm as it builds this independent set online is to maximize the sum of these (weighted rank) rewards. As in regular online analysis, we compare the rewards of our online algorithm to that of an offline optimum, namely a single independent set of the matroid that maximizes the sum of the weighted rank rewards that arrive over time. This problem is a natural extension of two well-studied streams of earlier work: the first is on online set cover algorithms (in particular for the max coverage version) while the second is on approximately maximizing submodular functions under a matroid constraint. In this paper, we present the first randomized online algorithms for this problem with poly-logarithmic competitive ratio. To do this, we employ the LP formulation of a scaled reward version of the problem. Then we extend a weighted-majority type update rule along with uncrossing properties of tight sets in the matroid polytope to find an approximately optimal fractional LP solution. We use the fractional solution values as probabilities for a online randomized rounding algorithm. To show that our rounding produces a sufficiently large reward independent set, we prove and use new covering properties for randomly rounded fractional solutions in the matroid polytope that may be of independent interest.

Original languageEnglish
Title of host publicationAutomata, Languages, and Programming - 39th International Colloquium, ICALP 2012, Proceedings
Number of pages12
EditionPART 1
StatePublished - 2012
Externally publishedYes
Event39th International Colloquium on Automata, Languages, and Programming, ICALP 2012 - Warwick, United Kingdom
Duration: 9 Jul 201213 Jul 2012

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
NumberPART 1
Volume7391 LNCS
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349


Conference39th International Colloquium on Automata, Languages, and Programming, ICALP 2012
Country/TerritoryUnited Kingdom


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