Random walk on the symplectic forms over a finite field

He, Jimmy

Algebraic Combinatorics, Tome 3 (2020) no. 5, pp. 1165-1181.

Random transvections generate a walk on the space of symplectic forms on ${\mathbf{F}}_q^{2n}$. The main result is to establish cutoff for this Markov chain. After $n+c$ steps, the walk is close to uniform while before $n-c$ steps, it is far from uniform. The upper bound is proved by explicitly finding and bounding the eigenvalues of the random walk. The lower bound is found by showing that the support of the walk is exponentially small if only $n-c$ steps are taken. The result can be viewed as a $q$-deformation of a result of Diaconis and Holmes on a random walk on matchings.

Classification : 60J10, 60B15, 20C33
Mots clés : Markov Chain, Gelfand Pair, Characteristic map, Symmetric functions

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