Extremal sizes of subspace partitions

A subspace partition Π of V?= V(n, q) is a collection of subspaces of V such that each 1-dimensional subspace of V is in exactly one subspace of Π. The size of Π is the number of its subspaces. Let σ _q (n, t) denote the minimum size of a subspace partition of V in which the largest subspace has dimension t, and let ρ _q (n, t) denote the maximum size of a subspace partition of V in which the smallest subspace has dimension t. In this article, we determine the values of σ _q (n, t) and ρ _q (n, t) for all positive integers n and t. Furthermore, we prove that if n ≥?2t, then the minimum size of a maximal partial t-spread in V(n +?t ?1, q) is σ _q (n, t).     

Set partitions with restrictions

Based on finite set partitions, we introduce restrictions to the distances among the elements in each part and refine the Stirling numbers of the second kind with an extra parameter in two different ways. Combinatorial approach through distributions of “balls into boxes” is employed to establish explicit formulae.     

Random partitions with restricted part sizes

For a subset of positive integers let Ω(n, ) be the set of partitions of n into summands that are elements of . For every λ ∈ Ω(n, ), let M _n(λ) be the number of parts, with multiplicity, that λ has. Put a uniform probability distribution on Ω(n, ), and regard M _n as a random variable. In this paper the limiting density of the (suitably normalized) random variable M _n is determined for sets that are sufficiently regular. In particular, our results cover the case = {Q(k) : k ≥ 1}, where Q(x) is a fixed polynomial of degree d ≥ 2. For specific choices of Q, the limiting density has appeared before in rather different contexts such as Kingman's coalescent, and processes associated with the maxima of Brownian bridge and Brownian meander processes. © 2007 Wiley Periodicals, Inc. Random Struct. Alg., 2008     

Set partitions and integrable hierarchies

We demonstrate that statistics for several types of set partitions are described by generating functions arising in the theory of integrable equations.     

Set partitions and moments of random variables

It is well known that the sequence of Bell numbers (Bn)_n?0 (Bn being the number of partitions of the set [n]) is the sequence of moments of a mean 1 Poisson random variable τ (a fact expressed in the Dobiński formula), and the shifted sequence (Bn+1)_n?0 is the sequence of moments of 1+τ. In this paper, we generalize these results by showing that both and (where is the number of m-partitions of [n], as they are defined in the paper) are moment sequences of certain random variables. Moreover, such sequences also are sequences of falling factorial moments of related random variables. Similar results are obtained when is replaced by the number of ordered m-partitions of [n]. In all cases, the respective random variables are constructed from sequences of independent standard Poisson processes.     

On certain unimodal sequences and strict partitions

Building on a bijection of Vandervelde, we enumerate certain unimodal sequences whose alternating sum equals zero. This enables us to refine the enumeration of strict partitions with respect to the number of parts and the BG-rank.     

A bijection between certain non-crossing partitions and sequences

We present a bijection between non-crossing partitions of the set [2n+1] into n+1 blocks such that no block contains two consecutive integers, and the set of sequences such that 1?s_i?i, and if s_i=j, then s_i-r?j-r for 1?r?j-1.     

Pairs of partitions without repeated odd parts

We prove two identities related to overpartition pairs. One of them gives a generalization of an identity due to Lovejoy, which was used in a joint work by Bringmann and Lovejoy to derive congruences for overpartition pairs. We apply our two identities on pairs of partitions where each partition has no repeated odd parts. We also present three partition statistics that give combinatorial explanations to a congruence modulo 3 satisfied by these partition pairs.     

On the number of distinct block sizes in partitions of a set

The average number of distinct block sizes in a partition of a set of n elements is asymptotic to e log n as n → ∞. In addition, almost all partitions have approximately e log n distinct block sizes. This is in striking contrast to the fact that the average total number of blocks in a partition is ～n(log n)^?1 as n → ∞.     

Divisibility of certain $$\ell $$ -regular partitions by 2

The Ramanujan Journal - For a positive integer $$\ell $$ , let $$b_{\ell }(n)$$ denote the number of $$\ell $$ -regular partitions of a nonnegative integer n. Motivated by some recent conjectures...     

Asymptotic results for partitions (I) and the distribution of certain integers

Asymptotic results, similar to those of Roth and Szekeres, are obtained for certain partition problems. These results are then applied to the distribution of integers of the form p₁^d₁p₂^d₂ … p_r^d_r, where d₁ ≥ d₂ ≥ … ≥ d_r, p_i denotes the ith prime and r is arbitrary. The saddle-point method is used to obtain the asymptotic results.     

Exponential decay of correlations for surface semi-flows without finite Markov partitions

We extend Dolgopyat's bounds on iterated transfer operators to suspensions of interval maps with infinitely many intervals of monotonicity.