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1 LaBRI - Laboratoire Bordelais de Recherche en Informatique 2 CEPAGE - Algorithmics for computationally intensive applications over wide scale distributed platforms Université Sciences et Technologies - Bordeaux 1, Inria Bordeaux - Sud-Ouest, École Nationale Supérieure d-Électronique, Informatique et Radiocommunications de Bordeaux ENSEIRB, CNRS - Centre National de la Recherche Scientifique : UMR5800 3 IUF - Institut Universitaire de France 4 LIAFA - Laboratoire d-informatique Algorithmique : Fondements et Applications 5 GANG - Networks, Graphs and Algorithms LIAFA - Laboratoire d-informatique Algorithmique : Fondements et Applications, Inria Paris-Rocquencourt

Abstract : This paper concerns graph spanners that approximate multipaths between pair of vertices of an undirected graphs with $n$ vertices. Classically, a spanner $H$ of stretch $s$ for a graph $G$ is a spanning subgraph such that the distance in $H$ between any two vertices is at most $s$ times the distance in $G$. We study in this paper spanners that approximate short cycles, and more generally $p$ edge-disjoint paths with $p>1$, between any pair of vertices. For every unweighted graph $G$, we construct a $2$-multipath $3$-spanner of $On^3-2$ edges. In other words, for any two vertices $u,v$ of $G$, the length of the shortest cycle with no edge replication traversing $u,v$ in the spanner is at most thrice the length of the shortest one in $G$. This construction is shown to be optimal in term of stretch and of size. In a second construction, we produce a $2$-multipath $2,8$-spanner of $On^3-2$ edges, i.e., the length of the shortest cycle traversing any two vertices have length at most twice the shortest length in $G$ plus eight. For arbitrary $p$, we observe that, for each integer $k\ge 1$, every weighted graph has a $p$-multipath $p2k-1$-spanner with $Op n^1+1-k$ edges, leaving open the question whether, with similar size, the stretch of the spanner can be reduced to $2k-1$ for all $p>1$.

Autor: Cyril Gavoille - Quentin Godfroy - Laurent Viennot -



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