# Connectivity of random k-nearest-neighbour graphs

## Abstract

Let P be a Poisson process intensity one a square Sn of area n. We construct a random geometric graph Gn,k by joining each point of P to its k ≡ k(n) nearest neighbours. Recently, Xue and Kumar proved that if k ≤ 0.074 log n then the probability that Gn,k is connected tends to 0 as n → ∞ while, if k ≥ 5.1774 log n, then the probability that Gn,k is connected tends to 1 as n → ∞. They conjectured that the threshold for connectivity is k = (1 + o(1)) log n. In this paper we improve these lower and upper bounds to 0.3043 log n and 0.5139 log n, respectively, disproving this conjecture. We also establish lower and upper bounds of 0.7209 log n and 0.9967 log n for the directed version of this problem. A related question concerns coverage. With Gn,k as above, we surround each vertex by the smallest (closed) disc containing its k nearest neighbours. We prove that if k ≤ 0.7209 log n then the probability that these discs cover Sn tends to 0 as n → ∞ while, if k ≥ 0.9967 log n, then the probability that the discs cover Sn tends to 1 as n → ∞. © Applied Probability Trust 2005.

## Publication Title

Advances in Applied Probability

## Recommended Citation

Balister, P., Bollobás, B., Sarkar, A., & Walters, M.
(2005). Connectivity of random k-nearest-neighbour graphs.* Advances in Applied Probability**, 37* (1), 1-24.
https://doi.org/10.1239/aap/1113402397