# Distribution-sensitive construction of the greedy spanner

S.P.A. Alewijnse, Q.W. Bouts, A.P. Brink, ten

2 Citaten (Scopus)

## Samenvatting

The greedy spanner is the highest quality geometric spanner (in e.g. edge count and weight, both in theory and practice) known to be computable in polynomial time. Unfortunately, all known algorithms for computing it on n points take O(n 2) time, limiting its use on large data sets. We observe that for many point sets, the greedy spanner has many ‘short’ edges that can be determined locally and usually quickly, and few or no ‘long’ edges that can usually be determined quickly using local information and the well-separated pair decomposition. We give experimental results showing large to massive performance increases over the state-of-the-art on nearly all tests and real-life data sets. On the theoretical side we prove a near-linear expected time bound on uniform point sets and a near-quadratic worst-case bound. Our bound for point sets drawn uniformly and independently at random in a square follows from a local characterization of t-spanners we give on such point sets: we give a geometric property that holds with high probability on such point sets. This property implies that if an edge set on these points has t-paths between pairs of points ‘close’ to each other, then it has t-paths between all pairs of points. This characterization gives a O(n log2 n log2 logn) expected time bound on our greedy spanner algorithm, making it the first subquadratic time algorithm for this problem on any interesting class of points. We also use this characterization to give a O((n¿+¿|E|) log2 n loglogn) expected time algorithm on uniformly distributed points that determines if E is a t-spanner, making it the first subquadratic time algorithm for this problem that does not make assumptions on E.
Originele taal-2 Engels Algorithms - ESA 2014 (22nd European Symposium on Algorithms, Wroclaw, Poland, September 8-10, 2014. Proceedings) A.S. Schulz, D. Wagner Berlin Springer 61-73 978-3-662-44776-5 https://doi.org/10.1007/978-3-662-44777-2_6 Gepubliceerd - 2014 22nd Annual European Symposium on Algorithms (ESA 2014) - Wrocław, PolenDuur: 8 sep 2014 → 10 sep 2014Congresnummer: 22

### Publicatie series

Naam Lecture Notes in Computer Science 8737 0302-9743

### Congres

Congres 22nd Annual European Symposium on Algorithms (ESA 2014) ESA 2014 Polen Wrocław 8/09/14 → 10/09/14 22nd European Symposium on Algorithms