Fast Construction of 4-Additive Spanners

A $k$-additive spanner of a graph is a subgraph that preserves the distance between any two nodes up to a total additive error of $+k$. Efficient algorithms have been devised for constructing 2 [Aingworth et al. SIAM '99], 6 [Baswana et al. ACM '10, Woodruff ICALP '13], and 8-additive spanners [Knudsen '17], but no efficient algorithms for 4-additive spanners have yet been discovered. In this paper we present a modification of Chechik's 4-additive spanner construction [Chechik SODA '13] that produces a 4-additive spanner on $\Oish(n^{7/5})$ edges, with an improved runtime of $\Oish(mn^{3/5})$ from $O(mn)$. We also discuss generalizations to the setting of weighted additive spanners.