蒙特卡罗方法计算定积分的进一步讨论

介绍了蒙特卡罗方法计算定积分的原理和方法.给出了用蒙特卡罗方法计算定积分的一个简单证明,从而揭示了蒙特卡罗方法和定积分定义间的内在联系.针对蒙特卡罗方法收敛慢的特点,提出将蒙特卡罗方法与相应的数值计算方法相结合,提高计算结果的精度.此外,将蒙特卡罗方法推广到反常积分上去.     

A Fast Numerical Method for Integral Equations of the First Kind with Logarithmic Kernel Using Mesh Grading

The aim of this paper is to develop a fast numerical method for two-dimensional boundary integral equations of the first kind with logarithm kernels when the boundary of the domain is smooth and closed. In this case, the use of the conventional boundary element methods gives linear systems with dense matrix. In this paper, we demonstrate that the dense matrix can be replaced by a sparse one if appropriate graded meshes are used in the quadrature rules. It will be demonstrated that this technique can increase the numerical efficiency significantly.     

The Integral Heisenberg Group as an Infinite Amalgam of Commutative Groups

The 2n-dimensional integral lattice, n > 1, equipped with the standard skew-symmetric 2-form additive with respect to each of the variables is considered. The family of all isotropic sublattices is studied. It is proved that the amalgam of this family of groups is the integral Heisenberg group.     

Repeating Use of Integral Transforms--A New Method for Evaluation of Some Infinite Integrals

A new method for evaluation of infinite integrals is proposed.The integrals are derived by applying the same or differentintegral transforms twice. The integral transforms of Laplace,Fourier, Mellin, Hankel, K, Y-Bessel, H-Struve, Stieltjes, generalizedStieltjes, Kantrovich and Lebedev were used. Using the proposedmethod, a number of new infinite integrals of elementary andspecial functions were derived.     

Computation of an infinite integral using series acceleration

A numerical computation in crystallography involves an infinite integral depending on one parameter. In a recent article in this journal this computational problem is addressed using Romberg’s method and tools for error control. One observe numerical difficulties with the reported approach both near the parameter’s endpoints and near the parameter interval’s midpoint. In this short note we will present an alternative approach making use of a known infinite series formulation of the problem at hand and a simple and efficient series acceleration technique. If some care is taken to avoid cancellations the numerical results are excellent for all values of the parameter. AMS subject classification 65B05, 65B10, 65D30     

无穷积分余项与其被积函数比值的收敛阶

对一类函数的无穷积分余项与该函数的比值得到当x趋于无穷大时的收敛阶,这类函数是幂函数与指数函数的乘积函数,并将其应用到Mittag-Leffler函数.同时考虑了对应的级数情形.     

无穷凹角区域各向异性问题的自然边界元法

本文研究无穷凹角区域上一类各向异性问题的自然边界元法.利用自然边界归化原理,获得该问题的Poisson积分公式和自然积分方程,给出了自然积分方程的数值方法,以及逼近解的收敛性和误差估计,最后给出了数值例子,以示方法的可行性和有效性.     

曲面积分的换元法

给出了曲面积分的换元法,丰富了曲面积分的计算方法.     

用于积分方程解的广义逆函数值Padé逼近的计算公式

首次建立了广义逆函数值Padé逼近的完整的计算公式函数值分子多项式和数量分母多项式的行列式公式。一个有用的存在条件借助于行列式形式得以给出。     

晶体微观结构的数值计算

晶体微观结构是晶体材料在特定物理条件下其多个能量极小平衔态在空间形成的某种微尺度的规则分布．几何非线性的连续介质力学理论可以用能量极小化原理来解释晶体微观结构的形成，并用Young测度来刻画平衡态各变体在空间的概率分布．定性的理解与定量地分析和计算晶体材料的微观结构对于发展和改进高级晶体功能材料，如形状记忆合金、铁电体、磁至伸缩材料等，有重要的意义．本文回顾了近年来晶体微观结构数值计算方面的最新进展．介绍了计算晶体微观结构的几种数值方法及有关的数值分析结果。     

广义对称性在积分计算中的应用

本文将积分计算中的对称性方法推广到了一般情形 ,并提出了通过适当改造被积函数以利用对称性来简化计算的方法 .     

积分型总极值方法的最优性条件

郑权提出了求总极值问题的积分—水平集的概念性算法,同时给出了最优性条件.本文构造函数F(x),讨论了该函数的性质,证明求解原问题等价于求解方程F(c)=0的根.在文中给出了相应的总极值存在的最优性条件.     

The use of the stochastic arithmetic to estimate the value of interpolation polynomial with optimal degree

One of the considerable discussions in data interpolation is to find the optimal number of data which minimizes the error of the interpolation polynomial. In this paper, first the theorems corresponding to the equidistant nodes and the roots of the Chebyshev polynomials are proved in order to estimate the accuracy of the interpolation polynomial, when the number of data increases. Based on these theorems, then we show that by using a perturbation method based on the CESTAC method, it is possible to find the optimal degree of the interpolation polynomial. The results of numerical experiments are presented.     

Computation of axisymmetric MHD flows in a channel with an external longitudinal magnetic field

A numerical study of two-dimensional plasma flows in coaxial channels of plasma accelerators is presented. Two new results are obtained. First, for the computation of MHD problems belonging to the class under consideration, Zalesak’s method is used. It is based on an explicit finite difference scheme with flux correction. This method is free of space splitting, and, therefore, is well suited for parallel computations on multiprocessors. Second, the statement of the problem is extended so that the acceleration of the plasma by the azimuth magnetic self-field goes on in the presence of an external longitudinal field. The results of test computations demonstrate the efficiency of the method and made it possible to investigate the influence of the longitudinal field on the properties of the plasma flows.     

有限体积法与多重网格法用于提高激波捕捉质量及加速收敛

多重网格技术是一种非常有效的数值计算方法，本文采用多重网格的ＦＡＳ格式进行数值实验，计算加速效果十分明显，同时，结合矢通量分裂用有限体积法，大大提高了主激波的质量。     

定积分计算方法及其数值试验

以定积分概念所蕴含的数学思想和哲学思想为指导,给出定积分近似计算的两种方法,即定义法和蒙特卡罗方法,并借助Matlab软件编程对其加以验证,数值试验结果显示所给方法可行且有效．     

关于定积分微元法的一点补充

通过一个实例提出问题,进而给出微元法中推导微元及检验微元表达式的简便方法.     

数据拟合函数的最小二乘积分法

数据拟合的方法很多,每种方法各有特点.本文探讨了积分准则下的数据拟合函数的方法,称为最小二乘积分法,并给出了两个常用拟合函数具体形式.     

Computation of Smooth Manifolds Via Rigorous Multi-parameter Continuation in Infinite Dimensions

In this paper, we introduce a constructive rigorous numerical method to compute smooth manifolds implicitly defined by infinite-dimensional nonlinear operators. We compute a simplicial triangulation of the manifold using a multi-parameter continuation method on a finite-dimensional projection. The triangulation is then used to construct local charts and an atlas of the manifold in the infinite-dimensional domain of the operator. The idea behind the construction of the smooth charts is to use the radii polynomial approach to verify the hypotheses of the uniform contraction principle over a simplex. The construction of the manifold is globalized by proving smoothness along the edge of adjacent simplices. We apply the method to compute portions of a two-dimensional manifold of equilibria of the Cahn–Hilliard equation.