The random assignment problem asks for the minimum-cost perfect matching in
the complete n×n bipartite graph \Knn with i.i.d. edge weights, say
uniform on [0,1]. In a remarkable work by Aldous (2001), the optimal cost was
shown to converge to ζ(2) as n→∞, as conjectured by M\'ezard and
Parisi (1987) through the so-called cavity method. The latter also suggested a
non-rigorous decentralized strategy for finding the optimum, which turned out
to be an instance of the Belief Propagation (BP) heuristic discussed by Pearl
(1987). In this paper we use the objective method to analyze the performance of
BP as the size of the underlying graph becomes large. Specifically, we
establish that the dynamic of BP on \Knn converges in distribution as
n→∞ to an appropriately defined dynamic on the Poisson Weighted
Infinite Tree, and we then prove correlation decay for this limiting dynamic.
As a consequence, we obtain that BP finds an asymptotically correct assignment
in O(n2) time only. This contrasts with both the worst-case upper bound for
convergence of BP derived by Bayati, Shah and Sharma (2005) and the best-known
computational cost of Θ(n3) achieved by Edmonds and Karp's algorithm
(1972).Comment: Mathematics of Operations Research (2009