اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدA versatile combinatorial approach of studying products of long cycles in symmetric groups
73
0
0.0
(
0
)
تأليف
Ricky X. F. Chen
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
In symmetric groups, studies of permutation factorizations or triples of permutations satisfying certain conditions have a long history. One particular interesting case is when two of the involved permutations are long cycles, for which many surprisingly simple formulas have been obtained. Here we combinatorially enumerate the pairs of long cycles whose product has a given cycle-type and separates certain elements, extending several lines of studies, and we obtain general quantitative relations. As consequences, in a unified way, we recover a number of results expecting simple combinatorial proofs, including results of Boccara (1980), Zagier (1995), Stanley (2011), F{e}ray and Vassilieva (2012), as well as Hultman (2014). We obtain a number of new results as well. In particular, for the first time, given a partition of a set, we obtain an explicit formula for the number of pairs of long cycles on the set such that the product of the long cycles does not mix the elements from distinct blocks of the partition and has an independently prescribed number of cycles for each block of elements. As applications, we obtain new explicit formulas concerning factorizations of any even permutation into long cycles and the first nontrivial explicit formula for computing strong separation probabilities solving an open problem of Stanley (2010).
قيم البحث
اقرأ أيضاً
We construct Menger subsets of the real line whose product is not Menger in the plane. In contrast to earlier constructions, our approach is purely combinatorial. The set theoretic hypothesis used in our construction is far milder than earlier ones,
and holds in all but the most exotic models of real set theory. On the other hand, we establish productive properties f
A connected digraph in which the in-degree of any vertex equals its out-degree is Eulerian; this baseline result is used as the basis of existence proofs for universal cycles (also known as ucycles or generalized deBruijn cycles or U-cycles) of sever
al combinatorial objects. The existence of ucycles is often dependent on the specific representation that we use for the combinatorial objects. For example, should we represent the subset ${2,5}$ of ${1,2,3,4,5}$ as 25 in a linear string? Is the representation 52 acceptable? Or it it tactically advantageous (and acceptable) to go with ${0,1,0,0,1}$? In this paper, we represent combinatorial objects as graphs, as in cite{bks}, and exhibit the flexibility and power of this representation to produce {it graph universal cycles}, or {it Gucycles}, for $k$-subsets of an $n$-set; permutations (and classes of permutations) of $[n]={1,2,ldots,n}$, and partitions of an $n$-set, thus revisiting the classes first studied in cite{cdg}. Under this graphical scheme, we will represent ${2,5}$ as the subgraph $A$ of $C_5$ with edge set consisting of ${2,3}$ and ${5,1}$, namely the second and fifth edges in $C_5$. Permutations are represented via their permutation graphs, and set partitions through disjoint unions of complete graphs.
We introduce a notion of the emph{crux} of a graph $G$, measuring the order of a smallest dense subgraph in $G$. This simple-looking notion leads to some generalisations of known results about cycles, offering an interesting paradigm of `replacing av
erage degree by crux. In particular, we prove that emph{every} graph contains a cycle of length linear in its crux. Long proved that every subgraph of a hypercube $Q^m$ (resp. discrete torus $C_3^m$) with average degree $d$ contains a path of length $2^{d/2}$ (resp. $2^{d/4}$), and conjectured that there should be a path of length $2^{d}-1$ (resp. $3^{d/2}-1$). As a corollary of our result, together with isoperimetric inequalities, we close these exponential gaps giving asymptotically optimal bounds on long paths in hypercubes, discrete tori, and more generally Hamming graphs. We also consider random subgraphs of $C_4$-free graphs and hypercubes, proving near optimal bounds on lengths of long cycles.
The emph{$q,t$-Catalan numbers} $C_n(q,t)$ are polynomials in $q$ and $t$ that reduce to the ordinary Catalan numbers when $q=t=1$. These polynomials have important connections to representation theory, algebraic geometry, and symmetric functions. Ha
glund and Haiman discovered combinatorial formulas for $C_n(q,t)$ as weighted sums of Dyck paths (or equivalently, integer partitions contained in a staircase shape). This paper undertakes a combinatorial investigation of the joint symmetry property $C_n(q,t)=C_n(t,q)$. We conjecture some structural decompositions of Dyck objects into mutually opposite subcollections that lead to a bijective explanation of joint symmetry in certain cases. A key new idea is the construction of infinite chains of partitions that are independent of $n$ but induce the joint symmetry for all $n$ simultaneously. Using these methods, we prove combinatorially that for $0leq kleq 9$ and all $n$, the terms in $C_n(q,t)$ of total degree $binom{n}{2}-k$ have the required symmetry property.
Let $G$ be an edge-coloured graph. The minimum colour degree $delta^c(G)$ of $G$ is the largest integer $k$ such that, for every vertex $v$, there are at least $k$ distinct colours on edges incident to $v$. We say that $G$ is properly coloured if no
two adjacent edges have the same colour. In this paper, we show that, for any $varepsilon >0$ and $n$ large, every edge-coloured graph $G$ with $delta^c(G) ge (1/2+varepsilon)n$ contains a properly coloured cycle of length at least $min{ n , lfloor 2 delta^c(G)/3 rfloor}$.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
