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arXiv 0907.1004math.CO
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交替排列的q- enumeration

A q-enumeration of alternating permutations

Matthieu Josuat-Vergès

摘要:

欧拉的一个经典结果指出正切数是欧拉数的交替和。Roselle的一个对偶结果指出,割线数可以通过有符号的乱序计数来获得。我们表明,这两个身份可以细化与以下统计:交叉排列和乱序的数量,以及在交替排列的模式31-2的数量。利用Corteel,Rubey,Prellberg和作者以前的结果,我们导出了q-正切数和q-正割数的闭公式。有两种不同的方法来获得这些公式:一种是用置换表,另一种是用加权Motzkin路径(Laguerre历史)。

英文摘要:

A classical result of Euler states that the tangent numbers are an alternating sum of Eulerian numbers. A dual result of Roselle states that the secant numbers can be obtained by a signed enumeration of derangements. We show that both identities can be refined with the following statistics: the number of crossings in permutations and derangements, and the number of patterns 31-2 in alternating permutations. Using previous results of Corteel, Rubey, Prellberg, and the author, we derive closed formulas for both q-tangent and q-secant numbers. There are two different methods to obtain these formulas: one with permutation tableaux and one with weighted Motzkin paths (Laguerre histories).

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