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arxiv: 1808.08892 · v2 · pith:54V6KGNGnew · submitted 2018-08-27 · 🧮 math.GR · math.PR

Random generation under the Ewens distribution

classification 🧮 math.GR math.PR
keywords alphadistributionewensneededpermutationscyclesewens-randomfixed
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The Ewens sampling formula with parameter $\alpha$ is the distribution on $S_n$ which gives each $\pi\in S_n$ weight proportional to $\alpha^{C(\pi)}$, where $C(\pi)$ is the number of cycles of $\pi$. We show that, for any fixed $\alpha$, two Ewens-random permutations generate at least $A_n$ with high probability. More generally we work out how many permutations are needed for $\alpha$ growing with $n$. Roughly speaking, two are needed for $0 \leq \alpha \ll n^{1/2}$, three for $n^{1/2} \ll \alpha \ll n^{2/3}$, etc.

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