Enumeration of Permutation Classes and Weighted Labelled Independent Sets

Discrete Mathematics & Theoretical Computer Science, vol. 22 no. 2, Permutation Patterns 2019.

Christian, Émile and Henning

A core graph In this paper, we study the staircase encoding of permutations, which maps a permutation to a staircase grid with cells filled with permutations. We consider many cases, where restricted to a permutation class, the staircase encoding becomes a bijection to its image. We describe the image of those restrictions using independent sets of graphs weighted with permutations. We derive the generating function for the independent sets and then for their weighted counterparts. The bijections we establish provide the enumeration of permutation classes. We use our results to uncover some unbalanced Wilf-equivalences of permutation classes and outline how to do random sampling in the permutation classes. In particular, we cover the classes Av(2314,3124) , Av(2413,3142), Av(2413,3124), Av(2413,2134) and Av(2314,2143), as well as many subclasses.

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