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32 Painlevé TranscendentsApplications

§32.14 Combinatorics

Let SN be the group of permutations 𝝅 of the numbers 1,2,…,N (§26.2). With 1≤m1<⋯<mn≤N, 𝝅⁡(m1),𝝅⁡(m2),…,𝝅⁡(mn) is said to be an increasing subsequence of 𝝅 of length n when 𝝅⁡(m1)<𝝅⁡(m2)<⋯<𝝅⁡(mn). Let ℓN⁡(𝝅) be the length of the longest increasing subsequence of 𝝅. Then

32.14.1 limN→∞Prob⁡(ℓN⁡(𝝅)−2⁢NN1/6≤s)=F⁡(s),

where the distribution function F⁡(s) is defined here by

32.14.2 F⁡(s)=exp⁡(−∫s∞(x−s)⁢w2⁡(x)⁢dx),

and w⁡(x) satisfies PII with α=0 and boundary conditions

32.14.3 w⁡(x) ∼Ai⁡(x),
x→+∞,
32.14.4 w⁡(x) ∼−12⁢x,
x→−∞,

where Ai denotes the Airy function (§9.2).

The distribution function F⁡(s) given by (32.14.2) arises in random matrix theory where it gives the limiting distribution for the normalized largest eigenvalue in the Gaussian Unitary Ensemble of n×n Hermitian matrices; see Tracy and Widom (1994).

See Forrester and Witte (2001, 2002) for other instances of Painlevé equations in random matrix theory.