How to Compute Times of Random Walks Based Distributed Algorithms

  • Authors:
  • Alain Bui;Devan Sohier

  • Affiliations:
  • SysCom - CReSTIC, Département de Mathématiques et Informatique, Université de Reims Champagne-Ardenne, BP1039 F-51687 Reims cedex, France. E-mail: {alain.bui,devan.sohier}@univ-reim ...;SysCom - CReSTIC, Département de Mathématiques et Informatique, Université de Reims Champagne-Ardenne, BP1039 F-51687 Reims cedex, France. E-mail: {alain.bui,devan.sohier}@univ-reim ...

  • Venue:
  • Fundamenta Informaticae
  • Year:
  • 2007

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Abstract

Random walk based distributed algorithms make use of a tokenthat circulates in the system according to a random walk scheme toachieve their goal. To study their efficiency and compare it to oneof the deterministic solutions, one is led to compute certainquantities, namely the hitting times and the cover time. Until now,only bounds on these quantities were known.First, this paper presents two generalizations of the notions ofhitting and cover times to weighted graphs. Indeed, the propertiesof random walks on symmetrically weighted graphs provideinteresting results on random walk based distributed algorithms,such as local load balancing. Both of these generalizations areproposed to precisely represent the behaviour of these algorithms,and to take into account what the weights represent.Then, we propose an algorithm to compute the n^2 hitting timeson a weighted graph of n vertices, which we improve to obtain aO(n^3) complexity. This complexity is the lowest up to now. Thisalgorithm computes both of the generalizations that we propose forthe hitting times on a weighted graph.Finally, we provide the first algorithm to compute the covertime (in both senses) of a graph. We improve it to achieve acomplexity of O(n^32^n). The algorithms that we present are allrobust to a topological change in a limited number of edges. Thisproperty allows us to use them on dynamic graphs.