辛Runge—Kutta方法的特征与构造

1 引 言 数值求解Hamilton系统时,冯康先生引进的辛方法能保持相空间辛结构,并使数值解继承Hamilton系统本身具有的许多重要特性。因而辛方法研究具有重要理论和实践意义。近年,Sanz-Serna等人深入研究了辛Runge-Kutta方法,在这方面作了系统的工作(参见[4,8—14])。 考虑s级Runge-Kutta方法     

膜自由振动的多辛方法

基于Hamilton空间体系的多辛理论研究了膜自由振动问题,讨论了构造复合离散多辛格式的方法,并构造了一种典型的9×3点半隐式的多辛复合离散格式,该格式满足多辛守恒律、能量守恒律和动量守恒律．数值算例结果表明该多辛离散格式具有较好的长时间数值稳定性．     

辛RK型方法的形式能量

引言 自从冯康先生创立哈密尔顿系统的辛算法后,为数众多且多种多样的保结构算法已经被提了出来［１－４］．哈密尔顿系统的能量Ｈ（ｚ）也是系统的不变量,但一般情况下,没有任何一个辛格式能够保持所有原始哈密尔顿能量［５,６］．另一方面,任何辛格式都保持一个形式哈密尔顿能量,它随格式本身的精度逼近原始哈密尔顿能量．关于形式能量的计算有多种途径,如冯康先生通过生成函数的微积分技巧在理论上得到了构造有生成函数确定的辛差分格式的形式能量的完整方法．Ｙｏｓｈ［１１］利用 Ｌｉｅ级数的 ＢＣＨ公式确定了可分哈密尔顿系…     

一种引力,电磁和自旋的非对偶统一场论

在Weyl, Eddington, Einstein和Schrdinger概念的框架中,经典统一场论常常不能令人信服,尤其找不到为什么Einstein-Maxwell(E-M)理论需要几何化的任何经验的理由.问题的关键并非是E-M理论是否完美,而是在经典意义下它能否回答现代的所有问题.特别是E-M理论不能提供一个经典理论框架,使Dirac方程能从其中导出,就象Schrdinger方程通过能量方程及对应原理从经典力学中导出一样.本文拟在这个如M.A.Tonnelat所提出的概念框架中,提出一种非对偶的统一场论(UFT).我们将度量式ds~2=g_(μ?)dx~(12)dx~(?)和非退化二次型F=(1/2!)·(?)dx~(?)dx(?)对称地引入理论,得到一种非对偶的统一场论.它包含了Einstein的广义相对论和狭义的Born-Infeld电动力学.尤其重要的是本文指出,采用对应原理,描述在“外部的”引力-电磁场中电子的Dirac方程,可以由非对偶Einstein方程通过简单因式分解导出.     

结构动力学方程的辛RK方法

针对有阻尼和外载荷的线性动力学常微分方程,给出了s级2s阶隐式Gauss-Legendre辛RK(Gauss-Legendre symplectic Runge-Kutta,GLSRK)方法的一种显式高效的执行格式,首次给出了Gauss-Legendre辛RK方法和经典RK方法(classical RK,CRK)的谱半径和单步相位误差的显式表达式,并将两者进行了比较.线性多自由度系统和非线性Rayleigh系统数值算例表明,对结构动力学系统而言,辛RK方法远比经典RK方法优越,在运动学特性和长时间数值模拟方面尤为明显.     

广义Boussinesq方程的多辛方法

广义Boussinesq方程作为一类重要的非线性方程有着许多有趣的性质,基于Hamilton空间体系的多辛理论研究了广义Boussinesq方程的数值解法,构造了一种等价于多辛Box格式的新隐式多辛格式,该格式满足多辛守恒律、局部能量守恒律和局部动量守恒律．对广义Boussinesq方程孤子解的数值模拟结果表明,该多辛离散格式具有较好的长时间数值稳定性．     

Landau-Ginzburg-Higgs方程的多辛Runge-Kutta方法

非线性波动方程作为一类重要的数学物理方程吸引着众多的研究者,基于Hamilton空间体系的多辛理论研究了Landau-Ginzburg-Higgs方程的多辛算法,讨论了利用Runge-Kutta方法构造离散多辛格式的途径,并构造了一种典型的半隐式的多辛格式,该格式满足多辛守恒律、局部能量守恒律和局部动量守恒律.数值算例结果表明该多辛离散格式具有较好的长时间数值稳定性.     

不可压饱和多孔弹性杆动力响应的多辛方法

研究了不可压饱和多孔弹性杆的一维动力响应问题.基于多孔介质理论,在流相和固相微观不可压、固相骨架小变形的假定下,建立了不可压流体饱和多孔弹性杆一维轴向动力响应的数学模型.利用Hamilton空间体系的多辛理论,构造了不可压饱和多孔弹性杆轴向振动方程的多辛形式及其多种局部守恒律.采用中点Box离散方法得到轴向振动方程的多辛离散格式和局部能量守恒律以及局部动量守恒律的离散格式;数值模拟了不可压饱和多孔弹性杆的轴向振动过程,记录了每一时间步的局部能量数值误差和局部动量数值误差.结果表明,已构造的多辛离散格式具有很高的精确性和较长时间的数值稳定性,这为解决饱和多孔介质的动力响应问题提供了新的途径.     

刚体动力学方程的一个辛积分方法

针对四元数和对应广义动量表示的刚体定点动力学方程,利用一种位移格式的微分—代数方程积分方案,实现了非独立广义动量表示的拉格朗日方程的辛积分算法．数值实验显示该算法具有精度高和保持系统守恒量的特点．更为重要的是,广义动量表示的拉格朗日方程较之传统形式的拉格朗日方程在辛积分中表现出独特的优越性．     

Gauge Field Fluxes and Bianchi Identities in Extended Field Theories

Theoretical and Mathematical Physics - The tensor hierarchy of exceptional field theories contains gauge fields satisfying certain Bianchi identities with sources determining the interactions with...     

Variational Discretizations of Gauge Field Theories Using Group-Equivariant Interpolation

Foundations of Computational Mathematics - We describe a systematic mathematical approach to the geometric discretization of gauge field theories that is based on Dirac and multi-Dirac mechanics...     

Associativity and Operator Hamiltonian Quantization of Gauge Theories

We show that the associative algebra structure can be incorporated in the BRST quantization formalism for gauge theories such that extension from the corresponding Lie algebra to the associative algebra is achieved using operator quantization of reducible gauge theories. The BRST differential that encodes the associativity of the algebra multiplication is constructed as a quadratic second-order differential operator on the bar resolution.     

Existence of 3D-Vortices in Abelian Gauge Theories

We consider the Abelian gauge theory related to the interaction between the solitary waves of the nonlinear Klein-Gordon equation and the electromagnetic field. We analyze the existence of electromagnetostatic solutions and, in particular, of vortices. Dedicated to the memory of Professor Aldo Cossu     

Magneto-Static Vortices in Two Dimensional Abelian Gauge Theories

We study the existence of vortices of the Klein-Gordon-Maxwell equations in the two dimensional case. In particular we find sufficient conditions for the existence of vortices in the magneto-static case, i.e. when the electric potential f = 0{\phi = 0}. This result, due to the lack of suitable embedding theorems for the vector potential A is achieved with the help of a penalization method.     

Towards an Operator-Algebraic Construction of Integrable Global Gauge Theories

The recent construction of integrable quantum field theories on two-dimensional Minkowski space by operator-algebraic methods is extended to models with a richer particle spectrum, including finitely many massive particle species transforming under a global gauge group. Starting from a two-particle S-matrix satisfying the usual requirements (unitarity, Yang–Baxter equation, Poincaré and gauge invariance, crossing symmetry, . . .), a pair of relatively wedge-local quantum fields is constructed which determines the field net of the model. Although the verification of the modular nuclearity condition as a criterion for the existence of local fields is not carried out in this paper, arguments are presented that suggest it holds in typical examples such as non-linear O(N)   σ-models. It is also shown that for all models complying with this condition, the presented construction solves the inverse scattering problem by recovering the S-matrix from the model via Haag–Ruelle scattering theory, and a proof of asymptotic completeness is given.     

Quasirenormalizable Quantum Field Theories

Theoretical and Mathematical Physics - Leading logarithms in massless nonrenormalizable effective field theories can be computed using nonlinear recurrence relations. These recurrence relations...     

Gauge Dependence of the Effective Gravitational Field

We analyze the gauge ambiguity problem for the effective gravitational field from the standpoint of the measurement process. The motion of a test point particle playing the role of a measuring device is investigated in the field of a point gravitating mass in the one-loop approximation. We show that the gravitational field value determined from the effective equations of motion of the device explicitly depends on the Feynman gauge parameter. This dependence is essential in the sense that a gauge variation cannot be interpreted as a deformation of the reference frame, which leads to a gauge ambiguity in the values of observed quantities. In particular, this result disproves the hypothesis that gauge dependence is canceled in the effective equations of motion of a classical point particle.     

线性Hamilton系统边值问题的保辛数值方法

以Hamilton系统的正则变换和生成函数为基础研究线性时变Hamilton系统边值问题的保辛数值求解算法.根据第二类生成函数系数矩阵与状态传递矩阵的关系,构造了生成函数系数矩阵的区段合并递推算法,并进一步将递推算法推广到线性非齐次边值问题中;然后利用生成函数的性质将边值问题转化为初值问题,最后采用初值问题的保辛算法求解以达到整个Hamilton系统保辛的目的.数值算例表明该方法能够有效地求解线性齐次与非齐次问题,并能很好地保持Hamilton系统的固有特性.