Right-jumps & pattern avoiding permutations

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TitreRight-jumps & pattern avoiding permutations
Type de publicationJournal Article
Year of Publication2016
AuteursBanderier C, Baril J-L, Santos CMoreira Do
JournalDISCRETE MATHEMATICS AND THEORETICAL COMPUTER SCIENCE
Volume18
Pagination12
Type of ArticleArticle
ISSN1462-7264
Mots-clésanalytic combinatorics, D-finite function, generating function, insertion sort, left-to-right maximum, Permutation pattern, supercongruence
Résumé

We study the iteration of the process of moving values to the right in permutations. We prove that the set of permutations obtained in this model after a given number of iterations from the identity is a class of pattern avoiding permutations. We characterize the elements of the basis of this class and enumerate it by giving their bivariate exponential generating function: we achieve this via a catalytic variable, the number of left-to-right maxima. We show that this generating function is a D-finite function satisfying a differential equation of order 2. We give some congruence properties for the coefficients of this generating function, and show that their asymptotics involves a rather unusual algebraic exponent (the golden ratio (1 + root 5)/2) and some closed-form constants. We end by proving a limit law: a forbidden pattern of length n has typically (ln n)/root 5 left-to-right maxima, with Gaussian fluctuations.