Distributions of statistics on separable permutations

We derive functional equations for distributions of six classical statistics (ascents, descents, left-to-right maxima, right-to-left maxima, left-to-right minima, and right-to-left minima) on separable and irreducible separable permutations. The equations are used to find a third degree equation for...

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Bibliographic Details
Published in:Discrete Applied Mathematics 2024-10, Vol.355, p.169-179
Main Authors: Chen, Joanna N., Kitaev, Sergey, Zhang, Philip B.
Format: Article
Language:English
Subjects:
Distribution
Irreducible permutation
Permutation statistic
Separable permutation
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Summary:We derive functional equations for distributions of six classical statistics (ascents, descents, left-to-right maxima, right-to-left maxima, left-to-right minima, and right-to-left minima) on separable and irreducible separable permutations. The equations are used to find a third degree equation for joint distribution of ascents and descents on separable permutations that generalizes the respective known result for the descent distribution. Moreover, our general functional equations allow us to derive explicitly (joint) distribution of any subset of maxima and minima statistics on irreducible, reducible and all separable permutations. In particular, there are two equivalence classes of distributions of a pair of maxima or minima statistics. Finally, we present three unimodality conjectures about distributions of statistics on separable permutations.
ISSN:0166-218X
1872-6771
DOI:10.1016/j.dam.2024.05.004