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arXiv 1111.5736math.CO
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1324和其他分层模式的Stanley Wilf极限的上界

Upper bounds for the Stanley-Wilf limit of 1324 and other layered patterns

Anders Claesson, Vít Jelínek, Einar Steingrímsson

摘要:

我们证明了任何长度为$\ell$的分层置换模式的Stanley-Wilf极限至多为$4\ell^2$,并且模式1324的Stanley-Wilf极限至多为16。这些界限来自一个更一般的结果,表明避免特殊形式的模式的排列是两个排列的合并,每个排列避免一个较小的模式。如果猜想是真的,长度为$\ell$的模式的最大斯坦利-威尔夫极限是通过分层模式获得的,则这意味着任何长度为$\ell$的模式的斯坦利-威尔夫极限的上界为$4\ell^2$。我们还推测,对于任何$k\ge 0$,具有$k$反转的1324-避免排列的集合包含至少与长度为$n$的排列一样多的长度为$n+1$的排列。我们证明,如果这是真的,那么斯坦利-威尔夫极限为1324是最多$e^{π\sqrt{2/3}} \simeq 13.001954$。

英文摘要:

We prove that the Stanley-Wilf limit of any layered permutation pattern of length $\ell$ is at most $4\ell^2$, and that the Stanley-Wilf limit of the pattern 1324 is at most 16. These bounds follow from a more general result showing that a permutation avoiding a pattern of a special form is a merge of two permutations, each of which avoids a smaller pattern. If the conjecture is true that the maximum Stanley-Wilf limit for patterns of length $\ell$ is attained by a layered pattern then this implies an upper bound of $4\ell^2$ for the Stanley-Wilf limit of any pattern of length $\ell$. We also conjecture that, for any $k\ge 0$, the set of 1324-avoiding permutations with $k$ inversions contains at least as many permutations of length $n+1$ as those of length $n$. We show that if this is true then the Stanley-Wilf limit for 1324 is at most $e^{π\sqrt{2/3}} \simeq 13.001954$.

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