English

Perfect partitions of a random set of integers

Combinatorics 2022-10-04 v1

Abstract

Let X1,,XnX_1,\dots, X_n be independent integers distributed uniformly on {1,,M}\{1,\dots, M\}, M=M(n)M=M(n)\to\infty however slow. A partition SS of [n][n] into ν\nu non-empty subsets S1,,SνS_1,\dots, S_{\nu} is called perfect, if all ν\nu values jS\aXj\sum_{j\in S_{\a}}X_j are equal. For a perfect partition to exist, jXj\sum_j X_j has to be divisible by ν\nu. For ν=2\nu=2, Borgs et al. proved, among other results, that, conditioned on jXj\sum_j X_j being even, with high probability a perfect partition exists if κ:=limnlogM>1log2\kappa:=\lim \tfrac{n}{\log M}>\tfrac{1}{\log 2}, and that w.h.p. no perfect partition exists if κ<1log2\kappa<\tfrac{1}{\log 2}. We prove that w.h.p. no perfect partition exists if ν3\nu\ge 3 and κ<2logν\kappa<\tfrac{2}{\log \nu}. We identify the range of κ\kappa in which the expected number of perfect partitions is exponentially high. We show that for κ>2(ν1)log[(12ν2)1]\kappa> \tfrac{2(\nu-1)}{\log[(1-2\nu^{-2})^{-1}]} the total number of perfect partitions is exponentially high with probability (1+ν2)1\gtrsim (1+\nu^2)^{-1}.

Keywords

Cite

@article{arxiv.2210.00656,
  title  = {Perfect partitions of a random set of integers},
  author = {Boris Pittel},
  journal= {arXiv preprint arXiv:2210.00656},
  year   = {2022}
}