English

Mallows permutations as stable matchings

Probability 2023-06-22 v2

Abstract

We show that the Mallows measure on permutations of 1,,n1,\ldots,n arises as the law of the unique Gale-Shapley stable matching of the random bipartite graph conditioned to be perfect, where preferences arise from a total ordering of the vertices but are restricted to the (random) edges of the graph. We extend this correspondence to infinite intervals, for which the situation is more intricate. We prove that almost surely every stable matching of the random bipartite graph obtained by performing Bernoulli percolation on the complete bipartite graph KZ,ZK_{\mathbb{Z},\mathbb{Z}} falls into one of two classes: a countable family (σn)nZ(\sigma_n)_{n\in\mathbb{Z}} of tame stable matchings, in which the length of the longest edge crossing kk is O(logk)O(\log |k|) as k±k\to\pm \infty, and an uncountable family of wild stable matchings, in which this length is expΩ(k)\exp \Omega(k) as k+k\to +\infty. The tame stable matching σn\sigma_n has the law of the Mallows permutation of Z\mathbb{Z} (as constructed by Gnedin and Olshanski) composed with the shift kk+nk\mapsto k+n. The permutation σn+1\sigma_{n+1} dominates σn\sigma_{n} pointwise, and the two permutations are related by a shift along a random strictly increasing sequence.

Keywords

Cite

@article{arxiv.1802.07142,
  title  = {Mallows permutations as stable matchings},
  author = {Omer Angel and Alexander E. Holroyd and Tom Hutchcroft and Avi Levy},
  journal= {arXiv preprint arXiv:1802.07142},
  year   = {2023}
}

Comments

22 pages, 7 figures. V2: Very minor revisions

R2 v1 2026-06-23T00:27:44.248Z