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| Content Provider | ACM Digital Library |
|---|---|
| Author | Coppersmith, Don Bollobás, Béla Elkin, Michael |
| Abstract | For an unweighted graph G = (V, E), G′ = (V, E′) is a subgraph if E′ ⊆ E, and G″ = (V″, E″, ω) is a Steiner graph if V ⊆ V″, and for any pair of vertices u, w ∈ V, the distance bet-ween them in G″(denoted dG″, (u, w)) is at least the distance between them in G (denoted da(u, w)).In this paperwe introduce the notion of distance preserver. A subgraph (resp., Steiner graph) G′ of a graph G is a subgraph (resp., Steiner) D-preserver of G if for every pair of vertices u, w ∈ V with dG(u, w) ≥ D, dG′, (u, w) = dG(u, w). We show that anygraph (resp., digraph) has a subgraph D-preserver with at most $O(n^{2}/D)$ edges (resp., arcs), and there are graphs and digraphs for which any undirected Steiner D-preserver contains $Ω(n^{2}/D)$ edges. However, we show that if one allows a directed Steiner (or, shortly, diS-teiner) D-preserver, then these bounds can be improved. Specifically, we show that for any graph or digraph there exists a diSteiner D-preserver with $O(n^{2}.log$ D/D.log n arcs, and that this result is tight up to a constant factor.We also study D-preserving distance labeling schemes, that are labeling schemes that guarantee precise calculation ofdistances between pairs of vertices that are at distance at least D one from another. We show that there exists a D-preserving labeling scheme with labels of size $O(n/Dlog^{2}$ n), and that labels of size Ω(n/D log D) are required for any D-preserving labeling scheme.Finally, we study additive spanners. A subgraph G′ of an undirected graph G = (V, E) is its additive β-spanner if for any pair of vertices u, w ∈ V, dG′, (u, w) ≤ dG(u, w)+β. It is known that for any n-vertex graph there exists an additive 2-spanner with $O(n^{3/2})$ edges, and an additive Steiner 4-spanner with $O(n^{4/3})$ edges. However, no construction of additive spanners with $o(n^{3/2})$ edges or Steiner additive spanners with $o(n^{4/3})$ edges are known so far. We devise a construction of additive $O(2^{1/Δ}n^{(1-Δ)}[1/Δ]--2/[1/Δ]--1)-spanner$ with $O(n^{1+Δ})$ edges for any graph and any Δ < 0. |
| Starting Page | 414 |
| Ending Page | 423 |
| Page Count | 10 |
| File Format | |
| ISBN | 0898715385 |
| Language | English |
| Publisher | Association for Computing Machinery (ACM) |
| Publisher Date | 2003-01-12 |
| Access Restriction | Subscribed |
| Content Type | Text |
| Resource Type | Article |
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