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Better Bounds for Coalescing-Branching Random Walks

Published: 13 June 2018 Publication History

Abstract

Coalescing-branching random walks, or cobra walks for short, are a natural variant of random walks on graphs that can model the spread of disease through contacts or the spread of information in networks. In a k-cobra walk, at each timestep, a subset of the vertices are active; each active vertex chooses k random neighbors (sampled independently and uniformly with replacement) that become active at the next step, and these are the only active vertices at the next step. A natural quantity to study for cobra walks is the cover time, which corresponds to the expected time when all nodes have become infected or received the disseminated information.
In this article, we extend previous results for cobra walks in multiple ways. We show that the cover time for the 2-cobra walk on [0,n]d is O(n) (where the order notation hides constant factors that depend on d); previous work had shown the cover time was O(n⋅polylog(n)). We show that the cover time for a 2-cobra walk on an n-vertex d-regular graph with conductance φG is O(d4φ−2Glog2n), significantly generalizing a previous result that held only for expander graphs with sufficiently high expansion. And, finally, we show that the cover time for a 2-cobra walk on a graph with n vertices and m edges is always O(mn3/4logn; this is the first result showing that the bound of Θ(n3) for the worst-case cover time for random walks can be beaten using 2-cobra walks.

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cover image ACM Transactions on Parallel Computing
ACM Transactions on Parallel Computing  Volume 5, Issue 1
Special Issue on SPAA 2016
March 2018
140 pages
ISSN:2329-4949
EISSN:2329-4957
DOI:10.1145/3232649
Issue’s Table of Contents
Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than the author(s) must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from [email protected].

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Association for Computing Machinery

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Publication History

Published: 13 June 2018
Accepted: 01 January 2018
Revised: 01 October 2017
Received: 01 March 2017
Published in TOPC Volume 5, Issue 1

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Author Tags

  1. Random walks
  2. cover time
  3. epidemic processes
  4. information spreading
  5. networks

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