TAILIEUCHUNG - Báo cáo toán học: "Matchings Avoiding Partial Patterns"

Tuyển tập các báo cáo nghiên cứu khoa học về toán học trên tạp chí toán học quốc tế đề tài: Matchings Avoiding Partial Patterns. | Matchings Avoiding Partial Patterns William Y. C. Chen1 Toufik Mansour2 Sherry H. F. Yan3 1 3Center for Combinatorics LPMC Nankai University Tianjin 300071 . China 2Department of Mathematics University of Haifa Haifa 31905 Israel 1chen@ 2toufik@ 3huifangyan@ Submitted Apr 16 2005 Accepted Dec 6 2006 Published Dec 18 2006 Mathematics Subject Classifications 05A05 05C30 Abstract We show that matchings avoiding a certain partial pattern are counted by the 3-Catalan numbers. We give a characterization of 12312-avoiding matchings in terms of restrictions on the corresponding oscillating tableaux. We also find a bijection between matchings avoiding both patterns 12312 and 121323 and Schroder paths without peaks at level one which are counted by the super-Catalan numbers or the little Schroder numbers. A refinement of the super-Catalan numbers is derived by fixing the number of crossings in the matchings. In the sense of Wilf-equivalence we use the method of generating trees to show that the patterns 12132 12123 12321 12231 12213 are all equivalent to the pattern 12312. 1 Introduction A matching on a set 2n 1 2 . 2ng is a partition of 2n in which every block contains exactly two elements or equivalently a graph on 2n in which every vertex has degree one. There are many ways to represent a matching. It can be displayed by drawing the 2n points on a horizontal line in the increasing order. This is called the linear representation of a matching 5 . An edge e i j in a matching is always written in such a way that i j where the vertices i and j are called the initial point and the endpoint respectively. We assume that every edge i j is drawn as an arc between the nodes i and j above the horizontal line. Let e i j and e0 i0 j0 be two edges of a matching M we say that e crosses e if they intersect with each other in other words if i i0 j j . In this case the pair of edges e and e is called a crossing of the matching. Otherwise e and e0 are

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