English

Random generation under the Ewens distribution

Group Theory 2019-01-23 v2 Probability

Abstract

The Ewens sampling formula with parameter α\alpha is the distribution on SnS_n which gives each πSn\pi\in S_n weight proportional to αC(π)\alpha^{C(\pi)}, where C(π)C(\pi) is the number of cycles of π\pi. We show that, for any fixed α\alpha, two Ewens-random permutations generate at least AnA_n with high probability. More generally we work out how many permutations are needed for α\alpha growing with nn. Roughly speaking, two are needed for 0αn1/20 \leq \alpha \ll n^{1/2}, three for n1/2αn2/3n^{1/2} \ll \alpha \ll n^{2/3}, etc.

Keywords

Cite

@article{arxiv.1808.08892,
  title  = {Random generation under the Ewens distribution},
  author = {Sean Eberhard},
  journal= {arXiv preprint arXiv:1808.08892},
  year   = {2019}
}

Comments

10 pages. Fixed typo

R2 v1 2026-06-23T03:44:58.081Z