Random Walks on Small World Networks

Abstract

We study the mixing time of random walks on small-world networks modelled as follows: starting with the 2-dimensional periodic grid, each pair of vertices $\{u,v\}$ with distance $d>1$ is added as a "long-range" edge with probability proportional to $d^{-r}$, where $r\ge 0$ is a parameter of the model. Kleinberg studied a close variant of this network model and proved that the (decentralised) routing time is $O((\log n{)}^2)$ when $r=2$ and $n^{\Omega (1)}$ when $r\ne 2$. Here, we prove that the random walk also undergoes a phase transition at $r=2$, but in this case the phase transition is of a different form. We establish that the mixing time is $\Theta (\log n)$ for $r<2$, $O((\log n{)}^4)$ for $r=2$ and $n^{\Omega (1)}$ for $r>2$.

To appear in Transactions of Algorithms (TALG)