196 research outputs found
On a refinement of Wilf-equivalence for permutations
Recently, Dokos et al. conjectured that for all , the patterns and
are -Wilf-equivalent. In this paper, we confirm this conjecture for all
and . In fact, we construct a descent set preserving bijection
between -avoiding permutations and -avoiding
permutations for all . As a corollary, our bijection enables us to
settle a conjecture of Gowravaram and Jagadeesan concerning the
Wilf-equivalence for permutations with given descent sets
Permutation patterns and statistics
Let S_n denote the symmetric group of all permutations of the set {1, 2,
...,n} and let S = \cup_{n\ge0} S_n. If Pi is a set of permutations, then we
let Av_n(Pi) be the set of permutations in S_n which avoid every permutation of
Pi in the sense of pattern avoidance. One of the celebrated notions in pattern
theory is that of Wilf-equivalence, where Pi and Pi' are Wilf equivalent if
#Av_n(Pi)=#Av_n(Pi') for all n\ge0. In a recent paper, Sagan and Savage
proposed studying a q-analogue of this concept defined as follows. Suppose
st:S->N is a permutation statistic where N represents the nonnegative integers.
Consider the corresponding generating function, F_n^{st}(Pi;q) = sum_{sigma in
Av_n(Pi)} q^{st sigma}, and call Pi,Pi' st-Wilf equivalent if
F_n^{st}(Pi;q)=F_n^{st}(Pi';q) for all n\ge0. We present the first in-depth
study of this concept for the inv and maj statistics. In particular, we
determine all inv- and maj-Wilf equivalences for any Pi containd in S_3. This
leads us to consider various q-analogues of the Catalan numbers, Fibonacci
numbers, triangular numbers, and powers of two. Our proof techniques use
lattice paths, integer partitions, and Foata's fundamental bijection. We also
answer a question about Mahonian pairs raised in the Sagan-Savage article.Comment: 28 pages, 5 figures, tightened up the exposition, noted that some of
the conjectures have been prove
Block patterns in Stirling permutations
We introduce and study a new notion of patterns in Stirling and -Stirling
permutations, which we call block patterns. We prove a general result which
allows us to compute generating functions for the occurrences of various block
patterns in terms of generating functions for the occurrences of patterns in
permutations. This result yields a number of applications involving, among
other things, Wilf equivalence of block patterns and a new interpretation of
Bessel polynomials. We also show how to interpret our results for a certain
class of labeled trees, which are in bijection with Stirling permutations
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