Symmetries in trees and parking functions

We investigate a particular symmetry in labeled trees first discovered by Gessel, which can be stated as follows: In the set of rooted labeled trees on n+1 vertices rooted at the smallest vertex, the number of trees with a descents and b+1 leaves equals the number of trees with b descents and a+1 leaves. We present two new ways to prove the symmetry resulting from decompositions of trees, which lead to three different bijections from trees to trees in which leaves and descents are swapped. We also interpret the symmetry in terms of parking functions: the number of parking functions on [n] with a descents and b unfavorable spaces (defined in this paper) equals the number of parking functions on [n] with b descents and a unfavorable spaces. We conclude with a generalization of these results to binary trees.RésuméNous étudions une symétrie particulière dans les arbres étiquetés, découverte par Gessel, qu'on peut énoncer comme suit: Dans l'ensemble des arbres étiquetés pointés avec n+1 sommets, pointés au sommet minimum, le nombre d'arbres avec a descentes et b+1 feuilles égale le nombre d'arbres avec b descentes et a+1 feuilles. Nous présentons deux nouvelles démonstrations de la symétrie, qui resultent des décompositions des arbres; à partir des décompositions, nous obtenons trois bijections des arbres sur les arbres qui échangent les feuilles et les descentes. De plus, nous interprétons la symétrie en termes des “fonctions de stationnement” (parking functions): le nombre des fonctions de stationnement avec a descentes et b positions défavorables (définies dans cette article) égale le nombre de fonctions de stationnement avec b positions défavorable et a descentes. Nous donnons aussi une généralisation de ces resultats aux arbres binaires.     

Symmetries for initial value problems

In this letter we give a less restrictive condition compared to that given by Zhang and Chen (2010), for first order initial conditions to be recoverable with a particular classical or nonclassical symmetry generator. Examples are provided for the generalised Kuramoto–Sivashinsky equation and a nonlinear diffusion equation with a sink term.     

Lie Symmetries and Weak Transversality

We discuss the notion of weak transversality and clarify its role in the context of Lie group theory with several examples. In particular, we present some new results concerning models of fluid dynamics.     

Symmetries of Linear and Linearizable Systems of Differential Equations

Symmetries (point, classical, and higher) of linear and linearizable differential equations and systems are studied, including the cases of ordinary equations, equations of the Burgers type, and Lax pairs.     

Symmetries of the WDVV Equations

We investigate the symmetry structure of the WDVV equations. We obtain an r-parameter group of symmetries, where r= (n ²+7n+4)+n/2. Moreover, it is proved that for n=3 and n=4 these comprise all symmetries. We determine a subgroup, which defines an SL₂-action on the space of solutions. For the special case n=3 this action is compared to the SL₂-symmetry of the Chazy equation. We construct similar solutions in the cases n=4 and n=5.     

Symmetries and Conservation Laws of the System: ux= vwx, vy= u wy, uv+wxx+wyy=0

After a short exposition of the theory of local and nonlocal symmetries and conservation laws for systems of PDEs, results on these and the recursion operator are listed for the system of PDEs u_x=vw_x, v_y=uw_y, uv+w_xx+w_yy=0. In between the methods of computation are explained.     

Essential Conservation Laws for Equations with Infinite Symmetries

We consider partial differential equations of variational problems with infinite symmetry groups. We study local conservation laws associated with arbitrary functions of one variable in the group generators. We show that only symmetries with arbitrary functions of dependent variables lead to an infinite number of conservation laws. We also calculate local conservation laws for the potential Zabolotskaya-Khokhlov equation for one of its infinite subgroups.__________Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 144, No. 1, pp. 190–198, July, 2005.     

Using Symmetries à Rebours

We consider nonclassical symmetries of partial differential equations (PDEs) in dimensions. Given a th‐order ordinary differential equation in the unknown we are able to find the most general scalar PDE of a given order which can be reduced via a nonclassical symmetry to .     

Symmetries of flat rank two distributions and sub-Riemannian structures

Flat sub-Riemannian structures are local approximations -- nilpotentizations -- of sub-Riemannian structures at regular points. Lie algebras of symmetries of flat maximal growth distributions and sub-Riemannian structures of rank two are computed in dimensions 3, 4, and 5.

     

分担四个小函数的亚纯函数的唯一性定理

设亚纯函数f和g分担四个小函数,如果(N)≤uT(r,f)+S(r,f)且(N) ≤(μ)T≤(μ)T(r,f)+S(r,f),(u, (μ))∈[0,1/16×[0,1/16),那么f=g.     

Möbius functions and semigroup representation theory

This paper explores several applications of Möbius functions to the representation theory of finite semigroups. We extend Solomon's approach to the semigroup algebra of a finite semilattice via Möbius functions to arbitrary finite inverse semigroups. This allows us to explicitly calculate the orthogonal central idempotents decomposing an inverse semigroup algebra into a direct product of matrix algebras over group rings. We also extend work of Bidigare, Hanlon, Rockmore and Brown on calculating eigenvalues of random walks associated to certain classes of finite semigroups; again Möbius functions play an important role.     

Chaotic Attractors with Discrete Planar Symmetries

Chaotic behavior is known to be compatible with symmetry and illustrations are constructed using functions equivariant with respect to the desired symmetries. Earlier investigations determined families of equivariant functions for a few of the discrete symmetry groups in the plane; those results are extended to all the discrete symmetry groups of the plane. This includes consideration of the all the frieze and two-dimensional crystallographic groups. © 1998 Elsevier Science Ltd. All rights reserved.     

On the Lie Algebras,Generalized Symmetries and Darboux Transformations of the Fifth-Order Evolution Equations in Shallow Water

By considering the one-dimensional model for describing long, small amplitude waves in shallow water, a generalized fifth-order evolution equation named the Olver water wave(OWW) equation is investigated by virtue of some new pseudo-potential systems. By introducing the corresponding pseudo-potential systems, the authors systematically construct some generalized symmetries that consider some new smooth functions{Xiβ}i=1,2,···,nβ =1,2,···,N depending on a finite number of partial derivatives of the nonlocal variables vβand a restriction ∑iα,β(? ξi/?vβ)2+(?ηα/?vβ)2≠0, i.e.,∑i,α,β(?Gα/?vβ)2≠0. Furthermore,the authors investigate some structures associated with the Olver water wave(AOWW)equations including Lie algebra and Darboux transformation. The results are also extended to AOWW equations such as Lax, Sawada-Kotera, Kaup-Kupershmidt, It and Caudrey-Dodd-Gibbon-Sawada-Kotera equations, et al. Finally, the symmetries are applied to investigate the initial value problems and Darboux transformations.     

Almost subadditive weight functions form Braun-Meise-Taylor theory of ultradistributions

As it is known, Roumieu-Komatsu theory of ultradistributions is strictly larger than Beurling-Björck one and that the latter theory is established by the class of all subadditive weight functions. In its own turn, Roumieu-Komatsu theory is equivalent to Braun-Meise-Taylor one which is given by the class of all weight functions. We prove that the class of all almost subadditive weight functions forms Braun-Meise-Taylor theory of ultradistributions.     

Conserved Quantities and Symmetries Related to Stochastic Dynamical Systems

The present article focuses on the three topics related to the notions of "conserved quantities" and "symmetries" in stochastic dynamical systems described by stochastic differential equations of Stratonovich type. The first topic is concerned with the relation between conserved quantities and symmetries in stochastic Hamilton dynamical systems, which is established in a way analogous to that in the deterministic Hamilton dynamical theory. In contrast with this, the second topic is devoted to investigate the procedures to derive conserved quantities from symmetries of stochastic dynamical systems without using either the Lagrangian or Hamiltonian structure. The results in these topics indicate that the notion of symmetries is useful for finding conserved quantities in various stochastic dynamical systems. As a further important application of symmetries, the third topic treats the similarity method to stochastic dynamical systems. That is, it is shown that the order of a stochastic system can be reduced, if the system admits symmetries. In each topic, some illustrative examples for stochastic dynamical systems and their conserved quantities and symmetries are given.     

Internal sets and internal functions in Colombeau theory

This paper is devoted to the study of generalized functions as pointwise functions (so-called internal functions) on certain sets of generalized points (so-called internal sets). We treat the case of the Colombeau algebras of generalized functions, for which these notions have turned out to constitute a fundamental technical tool. We provide general foundations for the notion of internal functions and internal sets and prove a saturation principle. Various applications to Colombeau algebras are given.     

基于截断tau的copula模型选择及应用

本文引进了截断tau,计论了它与生存阿基米德Copula之间的关系,并在此基础上提出一种新的选择Copula模型的方法,实例分析表明,这种构建Copula模型的方法较好反映了数据内在的信息,客观描述金融变量的相关性,便于尾部相关性分析,为金融市场相关性分析提供了一种新途径.     

Symmetries of Field Theories on the Noncommutative Plane

We report new developments concerning the symmetry properties and their actions on special solutions allowed by certain field theory models on the noncommutative plane. In particular, we seek Galilean-invariant models. The analysis indicates that this requirement strongly restricts the admissible interactions. Moreover, if a scalar field is coupled to a gauge field, then a geometric phase emerges for vortexlike solutions transformed by Galilean boosts.__________Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 144, No. 1, pp. 64–73, July, 2005.