Mathematics – Combinatorics
Scientific paper
2011-08-12
Mathematics
Combinatorics
25 pages. Presented at Permutation Patterns 2011. Associated Maple package posted at http://www.math.rutgers.edu/~baxter/paper
Scientific paper
We extend the notion of an enumeration scheme developed by Zeilberger and Vatter to the case of vincular patterns (also called "generalized patterns" or "dashed patterns"). In particular we provide an algorithm which takes in as input a set $B$ of vincular patterns and search parameters and returns a recurrence (called a "scheme") to compute the number of permutations of length $n$ avoiding $B$ or confirmation that no such scheme exists within the search parameters. We also prove that if $B$ contains only consecutive patterns and patterns of the form $\sigma_1\sigma_2 ... \sigma_{t-1}-\sigma_t$, then such a scheme must exist and provide the relevant search parameters. The algorithms are implemented in Maple and we provide empirical data on the number of small pattern sets admitting schemes. We make several conjectures on Wilf-classification based on this data. We also outline how to refine schemes to compute the number of $B$-avoiding permutations of length $n$ with $k$ inversions.
Baxter Andrew M.
Pudwell Lara K.
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