Patterns in random permutations avoiding the pattern 321

We consider a random permutation drawn from the set of 321 ‐avoiding permutations of length n and show that the number of occurrences of another pattern σ has a limit distribution, after scaling by n^{m + ?} where m is the length of σ and ? is the number of blocks in it. The limit is not normal, and can be expressed as a functional of a Brownian excursion.     

Structure of random 312‐avoiding permutations

We evaluate the probabilities of various events under the uniform distribution on the set of 312‐avoiding permutations of . We derive exact formulas for the probability that the i^th element of a random permutation is a specific value less than i, and for joint probabilities of two such events. In addition, we obtain asymptotic approximations to these probabilities for large N when the elements are not close to the boundaries or to each other. We also evaluate the probability that the graph of a random 312‐avoiding permutation has k specified decreasing points, and we show that for large N the points below the diagonal look like trajectories of a random walk. © 2015 Wiley Periodicals, Inc. Random Struct. Alg., 49, 599–631, 2016     

Almost perfect nonlinear families which are not equivalent to permutations

An important problem on almost perfect nonlinear (APN) functions is the existence of APN permutations on even-degree extensions of ${\mathbb{F}}_2$ larger than 6. Browning et al. (2010) gave the first known example of an APN permutation on the degree-6 extension of ${\mathbb{F}}_2$. The APN permutation is CCZ-equivalent to the previously known quadratic Kim κ-function (Browning et al. (2009)). Aside from the computer based CCZ-inequivalence results on known APN functions on even-degree extensions of ${\mathbb{F}}_2$ with extension degrees less than 12, no theoretical CCZ-inequivalence result on infinite families is known. In this paper, we show that Gold and Kasami APN functions are not CCZ-equivalent to permutations on infinitely many even-degree extensions of ${\mathbb{F}}_2$. In the Gold case, we show that Gold APN functions are not equivalent to permutations on any even-degree extension of ${\mathbb{F}}_2$, whereas in the Kasami case we are able to prove inequivalence results for every doubly-even-degree extension of ${\mathbb{F}}_2$.     

Pattern‐avoiding permutations and Brownian excursion part I: Shapes and fluctuations

Permutations that avoid given patterns are among the most classical objects in combinatorics and have strong connections to many fields of mathematics, computer science and biology. In this paper we study the scaling limits of a random permutation avoiding a pattern of length 3 and their relations to Brownian excursion. Exploring this connection to Brownian excursion allows us to strengthen the recent results of Madras and Pehlivan [25] and Miner and Pak [29] as well as to understand many of the interesting phenomena that had previously gone unexplained. © 2016 Wiley Periodicals, Inc. Random Struct. Alg., 50, 394–419, 2017     

Simple permutations and pattern restricted permutations

A simple permutation is one that does not map any non-trivial interval onto an interval. It is shown that, if the number of simple permutations in a pattern restricted class of permutations is finite, the class has an algebraic generating function and is defined by a finite set of restrictions. Some partial results on classes with an infinite number of simple permutations are given. Examples of results obtainable by the same techniques are given; in particular it is shown that every pattern restricted class properly contained in the 132-avoiding permutations has a rational generating function.     

Unfair permutations

We study unfair permutations, which are generated by letting $n$ players draw numbers and assuming that player $i$ draws $i$ times from the unit interval and records her largest value. This model is natural in the context of partitions: the score of the $i$th player corresponds to the multiplicity of the summand $i$ in a random partition, with the roles of minimum and maximum interchanged. We study the distribution of several parameters, namely the position of player $i$, the number of inversions, and the number of ascents. To perform some of the heavy computations, we use the computer algebra package Sigma.     

Baxter permutations

Chung et al. (1978) have proved that the number of Baxter permutations on [n] is

Viennot (1981) has then given a combinatorial proof of this formula, showing this sum corresponds to the distribution of these permutations according to their number of rises.

Cori et al. (1986), by making a correspondence between two families of planar maps, have shown that the number of alternating Baxter permutations on [2n+δ] is c_n+δc_n where c_n = (2n)!/(n + 1)!n! is the nth Catalan number.

In this paper, we establish a new one-to-one correspondence between Baxter permutations and three non-intersecting paths, which unifies Viennot (1981) and Cori et al. (1986). Moreover, we obtain more precise results for the enumeration of (alternating or not) Baxter permutations according to various parameters. So, we give a combinatorial interpretation of Mallows's formula (1979).     

Arc permutations

Arc permutations and unimodal permutations were introduced in the study of triangulations and characters. This paper studies combinatorial properties and structures on these permutations. First, both sets are characterized by pattern avoidance. It is also shown that arc permutations carry a natural affine Weyl group action, and that the number of geodesics between a distinguished pair of antipodes in the associated Schreier graph, and the number of maximal chains in the weak order on unimodal permutations, are both equal to twice the number of standard Young tableaux of shifted staircase shape. Finally, a bijection from non-unimodal arc permutations to Young tableaux of certain shapes, which preserves the descent set, is described and applied to deduce a conjectured character formula of Regev.     

Counting permutations

We give a direct count of the number of permutations of n objects for which (a) all the cycles have lengths divisible by a fixed integer d, and (b) none of the cycles has length divisible by d.     

Five discordant permutations

A permutation π of1,2, …,π is5-discordant if π(i) ≠i, i + 1,i + 2, i + 3, i + 4 modn for 1 ≤i ≤n. A system of recurrences for computing the rook polynomials associated with5-discordant permutations is derived. This system, together with hit polynomials enable the5-discordant permutations to be enumerated.     

Quasirandom arithmetic permutations

In [J.N. Cooper, Quasirandom permutations, 2002, to appear], the author introduced quasirandom permutations, permutations of Z_n which map intervals to sets with low discrepancy. Here we show that several natural number-theoretic permutations are quasirandom, some very strongly so. Quasirandomness is established via discrete Fourier analysis and the Erd?s-Turán inequality, as well as by other means. We apply our results on Sós permutations to make progress on a number of questions relating to the sequence of fractional parts of multiples of an irrational. Several intriguing open problems are presented throughout the discussion.     

Sequences generating permutations

Linear recurring sequences generating permutations of the elements of a finite ring are introduced and examined. A complete answer to the discussed problems is given for the second-order sequences over Z_M. The possibilities for applications are also discussed.     

On TDP permutations

A permutation :i| _i , 0i<n is called a TDP permutation ifi–a _i j–a _j (modn) fori j. This paper finds all TDP permutations forn15, discusses the method for generating TDP permutations, and finally by applying MLE method obtains a formula for estimating the number of TDP permutations forn> 15.Project supported by National Natural Science Foundation of China.