English

The distribution on permutations induced by a random parking function

Probability 2024-06-19 v5 Combinatorics

Abstract

A parking function on [n][n] creates a permutation in SnS_n via the order in which the nn cars appear in the nn parking spaces. Placing the uniform probability measure on the set of parking functions on [n][n] induces a probability measure on SnS_n. We initiate a study of some properties of this distribution. Let PnparkP_n^{\text{park}} denote this distribution on SnS_n and let PnP_n denote the uniform distribution on SnS_n. In particular, we obtain an explicit formula for Pnpark(σ)P_n^{\text{park}}(\sigma) for all σSn\sigma\in S_n. Then we show that for all but an asymptotically PnP_n-negligible set of permutations, one has Pnpark(σ)((2ϵ)n(n+1)n1,(2+ϵ)n(n+1)n1)P_n^{\text{park}}(\sigma)\in\left(\frac{(2-\epsilon)^n}{(n+1)^{n-1}},\frac{(2+\epsilon)^n}{(n+1)^{n-1}}\right). However, this accounts for only an exponentially small part of the PnparkP_n^{\text{park}}-probability. We also obtain an explicit formula for Pnpark(σnj+11=i1,σnj+21=i2,,σn1=ij)P_n^{\text{park}}(\sigma^{-1}_{n-j+1}=i_1,\sigma^{-1}_{n-j+2}=i_2,\cdots, \sigma^{-1}_n=i_j), the probability that the last jj cars park in positions i1,,iji_1,\cdots, i_j respectively, and show that the jj-dimensional random vector (n+1σnj+l1,n+1σnj+21,,n+1σn1)(n+1-\sigma^{-1}_{n-j+l}, n+1-\sigma^{-1}_{n-j+2},\cdots, n+1-\sigma^{-1}_{n}) under PnparkP_n^{\text{park}} converges in distribution to a random vector (r=1jXr,r=2jXr,,Xj1+Xj,Xj)(\sum_{r=1}^jX_r,\sum_{r=2}^j X_r,\cdots, X_{j-1}+X_j,X_j), where {Xr}r=1j\{X_r\}_{r=1}^j are IID with the Borel distribution. We then show that in fact for jn=o(n16)j_n=o(n^\frac16), the final jnj_n cars will park in increasing order with probability approaching 1 as nn\to\infty. We also obtain an explicit formula for the expected value of the left-to-right maximum statistic XnLR-maxX_n^{\text{LR-max}}, which counts the total number of left-to-right maxima in a permutation, and show that EnparkXnLR-maxE_n^{\text{park}}X_n^{\text{LR-max}} grows approximately on the order n12n^\frac12.

Keywords

Cite

@article{arxiv.2404.11529,
  title  = {The distribution on permutations induced by a random parking function},
  author = {Ross G. Pinsky},
  journal= {arXiv preprint arXiv:2404.11529},
  year   = {2024}
}

Comments

In this version, results concerning the left-to-right maximum statistic have been added to the paper

R2 v1 2026-06-28T15:57:33.018Z