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Proceedings of 37th Conference on Foundations of Computer Science (1996)
Burlington, VT
Oct. 14, 1996 to Oct. 16, 1996
ISBN: 0-8186-7594-2
pp: 452
D. Dor , Dept. of Comput. Sci., Tel Aviv Univ., Israel
S. Halperin , Dept. of Comput. Sci., Tel Aviv Univ., Israel
U. Zwick , Dept. of Comput. Sci., Tel Aviv Univ., Israel
ABSTRACT
Let G=(V,E) be an unweighted undirected graph on n vertices. A simple argument shows that computing all distances in G with an additive one-sided error of at most 1 is as hard as Boolean matrix multiplication. Building on recent work of D. Aingworth et al. (1996), we describe an O/spl tilde/(min{n/sup 3/2/m/sup 1/2/,n/sup 7/3/}) time algorithm APASP/sub 2/ for computing all distances in G with an additive one-sided error of at most 2. The algorithm APASP/sub 2/ is simple, easy to implement, and faster than the fastest known matrix multiplication algorithm. Furthermore, for every even k>2, we describe an O/spl tilde/(min{n/sup 2-(2)/(k+2)/m/sup (2)/(k+2)/, n/sup 2+(2)/(3k-2)/}) time algorithm APASP/sub k/ for computing all distances in G with an additive one-sided error of at most k. We also give an O/spl tilde/(n/sup 2/) time algorithm APASP/sub /spl infin// for producing stretch 3 estimated distances in an unweighted and undirected graph on n vertices. No constant stretch factor was previously achieved in O/spl tilde/(n/sup 2/) time. We say that a weighted graph F=(V,E') k-emulates an unweighted graph G=(V,E) if for every u, v/spl isin/V we have /spl delta//sub G/(u,v)/spl les//spl delta//sub F/(u,v)/spl les//spl delta//sub G/(u,v)+k. We show that every unweighted graph on n vertices has a 2-emulator with O/spl tilde/(n/sup 3/2/) edges and a 4-emulator with O/spl tilde/(n/sup 4/3/) edges. These results are asymptotically tight. Finally, we show that any weighted undirected graph on n vertices has a 3-spanner with O/spl tilde/(n/sup 3/2/) edges and that such a 3-spanner can be built in O/spl tilde/(mn/sup 1/2/) time. We also describe an O/spl tilde/(n(m/sup 2/3/+n)) time algorithm for estimating all distances in a weighted undirected graph on n vertices with a stretch factor of at most 3.
INDEX TERMS
matrix multiplication; all pairs almost shortest paths; unweighted undirected graph; vertices; Boolean matrix multiplication; matrix multiplication algorithm; 3-spanner; weighted undirected graph
CITATION

U. Zwick, D. Dor and S. Halperin, "All pairs almost shortest paths," Proceedings of 37th Conference on Foundations of Computer Science(FOCS), Burlington, VT, 1996, pp. 452.
doi:10.1109/SFCS.1996.548504