English

A Chinese restaurant process for multiset permutations

Probability 2026-02-17 v3

Abstract

Multisets are like sets, except that they can contain multiple copies of their elements. If there are nin_i copies of ii, 1it1\leq i\leq t, in multiset MtM_t, then there are (n1++ntn1,,nt)\binom{n_1+\cdots+n_t}{n_1,\ldots, n_t} possible permutations of MtM_t. Knuth showed how to factor any multiset permutation into cycles. For fixed nin_i, i1i\geq 1, we show how to adapt the Chinese restaurant process, which generates random permutations on nn elements with weighting θ#cycles\theta^{\# \, {\rm cycles}}, θ>0\theta>0, sequentially for n=1,2,n=1,2,\ldots, to the multiset case, where we fix the nin_i and build permutations on MtM_t sequentially for t=1,2,t=1,2,\ldots. The number of cycles of a multiset permutation chosen uniformly at random, i.e.~θ=1\theta=1, has distribution given by the sum of independent negative hypergeometric distributed random variables. For all θ>0\theta>0, and under the assumption that ni=O(1)n_i=O(1), we show a central limit theorem as tt\to\infty for the number of cycles.

Keywords

Cite

@article{arxiv.2509.13979,
  title  = {A Chinese restaurant process for multiset permutations},
  author = {Dudley Stark},
  journal= {arXiv preprint arXiv:2509.13979},
  year   = {2026}
}

Comments

13 pages, accepted version

R2 v1 2026-07-01T05:41:55.400Z