id: 00672304 dt: j an: 00672304 au: Donnelly, Peter; Lloyd, Peter; Sudbury, Aidan ti: Approach to stationarity of the Bernoulli-Laplace diffusion model. so: Adv. Appl. Probab. 26, No.3, 715-727 (1994). py: 1994 pu: Applied Probability Trust, Sheffield la: EN cc: ut: distance transitive graph; Eberlein polynomials; exclusion process; Johnson graph; transition probabilities; separation distance; transient distribution; equilibrium distribution; cut-off phenomenon ci: li: doi:10.2307/1427817 ab: Summary: Two urns initially contain $r$ red balls and $n-r$ black balls respectively. At each time epoch a ball is chosen randomly from each urn and the balls are switched. Effectively the same process arises in many other contexts, notably for a symmetric exclusion process and random walk on the Johnson graph. If $Y(\cdot)$ counts the number of black balls in the first urn then we give a direct asymptotic analysis of its transition probabilities to show that (when run at rate $(n-r)/n$ in continuous time) for $j= αn+ o(n)$, $r= βn+ o(n)$, $0\leqα\leqβ\leq {1\over 2}$, $β>0$, $${\bold P} (Y(\log n+c)= j)/ π\sb n(j)\to \exp (γ\sb αe\sp{-c}) \quad \text{as} \quad n\to\infty,$$ where $π\sb n$ denotes the equilibrium distribution of $Y(\cdot)$ and $γ\sb α= 1-α/ β(1- β)$. Thus for large $n$ the transient probabilities approach their equilibrium values at time $\log n+ \log \vert γ\sb α\vert$ $(\leq\log n)$ in a particularly sharp manner. The same is true of the separation distance between the transient distribution and the equilibrium distribution. This is an explicit analysis of the so-called cut-off phenomenon associated with a wide variety of Markov chains. rv: