Counting segmented permutations using bicoloured Dyck paths

Anders Claesson

Research output: Contribution to journalArticle

Abstract

A bicoloured Dyck path is a Dyck path in which each up-step is assigned one of two colours, say, red and green. We say that a permutation π is σ-segmented if every occurrence o of σ in π is a segment-occurrence (i.e., o is a contiguous subword in π).

We show combinatorially the following two results: The 132-segmented permutations of length n with k occurrences of 132 are in one-to-one correspondence with bicoloured Dyck paths of length 2n−4k with k red up-steps. Similarly, the 123-segmented permutations of length n with k occurrences of 123 are in one-to-one correspondence with bicoloured Dyck paths of length 2n−4k with k red up-steps, each of height less than 2.

We enumerate the permutations above by enumerating the corresponding bicoloured Dyck paths. More generally, we present a bivariate generating function for the number of bicoloured Dyck paths of length 2n with k red up-steps, each of height less than h. This generating function is expressed in terms of Chebyshev polynomials of the second kind.
Original languageEnglish
Article numberR39
Number of pages18
JournalThe Electronic Journal of Combinatorics
Volume12
Publication statusPublished - 17 Aug 2005

Keywords

  • bicoloured Dyck path
  • Dyck path
  • segmented permutations

Fingerprint Dive into the research topics of 'Counting segmented permutations using bicoloured Dyck paths'. Together they form a unique fingerprint.

  • Cite this