Abstract

Symmetric joint distribution between crossings and nestings was established in several combinatorial objects. Recently, Marberg extended Chen and Guo's result on coloured matchings to coloured set partitions following a multi-dimensional generalization of the bijection and enumerative methods from Chen, Deng, Du, Stanley, and Yan. We complete the study for arc-coloured permutations by establishing symmetric joint distribution for crossings and nestings and by showing that the ordinary generating functions for $j$-noncrossing, $k$-nonnesting, $r$-coloured permutations according to size $n$ are rational functions. Finally, we automate the generation of these rational functions and analyse the first $70$ series.

Highlights

  • Crossing and nesting statistics have intrigued combinatorialists for many decades

  • We show that the ordinary generating functions for j-noncrossing, k-nonnesting, r-coloured permutations according to size n are rational functions, and automate the generation of these rational functions

  • With automated generation of their rational series according to crossing and nesting statistics, random generation algorithms like Boltzmann sampling [9] can be applied for the investigation of the distribution of such structures modelled by coloured permutations

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Summary

Introduction

Crossing and nesting statistics have intrigued combinatorialists for many decades. For example, it is well known that. On coloured set partitions, we combine two theorems of [14] to establish symmetric joint the electronic journal of combinatorics 22(1) (2015), #P1.14 distribution of crossing and nesting statistics for arc-coloured permutations. We show that the ordinary generating functions for j-noncrossing, k-nonnesting, r-coloured permutations according to size n are rational functions, and automate the generation of these rational functions. R-coloured permutations may be a natural model for the study of genome rearrangement problems, in particular, for tracking different types of distance metrics [10]. With automated generation of their rational series according to crossing and nesting statistics, random generation algorithms like Boltzmann sampling [9] can be applied for the investigation of the distribution of such structures modelled by coloured permutations

Definitions and terminology
An extension to coloured permutations
Background
Encoding process
An example of a 2-coloured permutation
Enumeration of coloured set partitions—another approach
Enumeration of r-coloured permutations
Warm-up examples
Proof of Rationality through Multigraphs for r-coloured permutations
Observations from 70 initial series
Noncrossing permutations
A non-D-finite conjecture
Permutations of type B
Findings
Concluding Remarks
Full Text
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