Additive Spanners and (alpha, beta)-Spanners

Baswana, Surender and Kavitha, Telikepalli and Mehlhorn, Kurt and Pettie, Seth (2011) Additive Spanners and (alpha, beta)-Spanners. In: ACM Transactions on Algorithms, 7 (1).

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Abstract

An (alpha, beta)-spanner of an unweighted graph G is a subgraph H that distorts distances in G up to a multiplicative factor of a and an additive term beta. It is well known that any graph contains a (multiplicative) (2k - 1, 0)-spanner of size O(n(1+1/k)) and an (additive) (1, 2)-spanner of size O(n(3/2)). However no other additive spanners are known to exist. In this article we develop a couple of new techniques for constructing (alpha, beta)-spanners. Our first result is an additive (1, 6)-spanner of size O(n(4/3)). The construction algorithm can be understood as an economical agent that assigns costs and values to paths in the graph, purchasing affordable paths and ignoring expensive ones, which are intuitively well approximated by paths already purchased. We show that this path buying algorithm can be parameterized in different ways to yield other sparseness-distortion tradeoffs. Our second result addresses the problem of which (alpha, beta)-spanners can be computed efficiently, ideally in linear time. We show that, for any k, a (k, k - 1)-spanner with size O(kn(1+1/k)) can be found in linear time, and, further, that in a distributed network the algorithm terminates in a constant number of rounds. Previous spanner constructions with similar performance had roughly twice the multiplicative distortion.

Item Type:	Journal Article
Publication:	ACM Transactions on Algorithms
Publisher:	Association for Computing Machinery
Additional Information:	Copyright of this article belongs to Association for Computing Machinery.
Keywords:	Spanner;metric embedding
Department/Centre:	Division of Electrical Sciences > Computer Science & Automation
Date Deposited:	12 Apr 2011 07:57
Last Modified:	12 Apr 2011 07:57
URI:	http://eprints.iisc.ac.in/id/eprint/36775

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