一类重积分解法的探讨

从一道考研试题入手,给出了当二重积分的被积函数或积分区域边界含x2-y2时的"双曲坐标变换"法.通过实例,对比说明该方法能够解决一类用直角坐标不易计算或不能计算的二重积分问题,并且可以运用到三重积分的计算上.     

重积分和线面积分中的一个典型题目

针对授课班级出错率较高的一道曲面积分题目,给出四种解法.分析出错的原因在于练习不够外,主要是对重积分概念理解不够透彻.     

由一道例题透析三重积分的解法

本文通过一道例题的多种解法透析三重积分计算中常用的截面法、投影法、利用柱坐标、球坐标和高斯公式求解三重积分.     

重积分的变换技巧

重积分的变换方法灵活,技巧性强,最理想的变换是把由曲线围成的区域变成短形区域或直边形区域,通常称作“化曲为方”或“化曲为直”．但同时还要考虑使被积函数易于求累次积分,即设法将积分区域及被积函数“化繁为简”．例如：求积分其中D是由坐标轴及抛物线所围成的区域（a,b＞0）．解在直角坐标系中D可用不等式组表为本题也可以采用各种不同的变量代换,虽然选择各种变换具有一定的难度和技巧,但从中可以灵活掌握各种变换的思想方法,训练适当选择变换的基本功．变换1（化曲为方）此变换将、平面上的曲边三角形区域D变成平面上的…     

利用重积分证明定积分不等式

利用重积分与定积分的关系,举例说明利用重积分证明定积分不等式。     

利用二重积分解定积分问题

通过实例介绍如何用二重积分计算某些特殊的定积分．为定积分的计算提供一种思路,展示了二重积分与定积分在一定程度上的内在联系．     

化重积分为累次积分的压缩法

本文从重积分的物理意义出发，运用“压缩法”得到了化重积分为累次积分的计算公式。     

关于重积分与线面积分内容体系的探讨

本文将二重积分、三重积分、第一类曲线积分及第一类曲面积分统一为多元数量值函数的积分，并且用第一类曲线、曲面积分定义第二类曲线、曲面积分。     

第一型曲面积分的一题多解

基于元素法和积分的性质讨论了第一型曲面积分的一题多解.     

一类曲面积分的解法

本文对定义在柱面上的一类函数给出了用定积分求曲面积分的方法 ,并证明了方法的可行性 .     

Fast Iterative Methods for Solving of Boundary Nonlinear Integral Equations with Singularity

A very efficient and fully discrete method for numerical solution of boundary nonlinear integral equation is described. There seems a lack of rigorous numerical analysis because of singular or hypersingular behavior. In this paper, we suggest variants of methods for solving numerical solutions. Moreover, our aim has been to show how the iterations can be effectively and efficiently regularized for solving ill-posed problems by using the preconditioner. We have compared these methods with CPU time and iterations. Finally, some numerical examples show the efficiency of the proposed methods.     

再生核空间中一类非线性积分方程的求解方法

本文在再生核空间中,利用再生核把非线性积分方程化为线性积分方程,研究了此类方程的求解问题,揭示了此类方程解的结构,存在性及多解等问题.     

关于一个二重积分计算公式

约定f为连续函数,分别利用交换积分次序、变量替换、等位线法等三种方法证明二重积分计算公式∫0^a∫0^a f（x＋y）dxdy=∫0^a（a-t）f（t＋a）dt＋∫0^atf（t）dt,并得到一个类似公式∫0^a∫0^af（x-y）dxdy=∫0^atf（t-a）dt＋∫0^a（a-t）f（t）dt.     

用积分方程法解板的振动问题*

本文把带有集中质量、弹性支承和弹簧支撑着的质量块(振子)的薄板的振动微分方程化成为积分方程的特征值问题。然后利用广义函数理论和积分方程理论,得到了用一无穷阶矩阵的标准特征值形式给出的频率方程,从而方便地得到了固有频率和振型。并讨论了这种方法的收敛性。     

多元积分方程自适应解法的优化

给出了核属于Besov空间的第二类Fredholm积分方程自适应的最优算法,并得到相关的误差阶的精确估计。     

Discontinuous Galerkin Methods for Solving a Frictional Contact Problem with Normal Compliance

Abstract

Several discontinuous Galerkin (DG) methods are introduced for solving a frictional contact problem with normal compliance, which is modeled as a quasi-variational inequality. Consistency, boundedness, and stability are established for the DG methods. Two numerical examples are presented to illustrate the performance of the DG methods.     

一道Lebesgue积分题目的注记

设E为n维欧氏空间Rn的可测子集,m E+∞,f(x)为E上的非负可测函数,并记Ek=E{x|k≤f(x)k+1}(k=0,1,2,…),利用Lebesgue积分的性质,通过构造反例,指出"级数∑k km Ek收敛"并不是f(x)在E上Lebesgue可积的充分条件.进一步,通过增加条件"f在E上a.e.有限",得到相应的充分必要条件.     

Implications of the Choice of Quadrature Nodes for Picard Integral Deferred Corrections Methods for Ordinary Differential Equations

This paper concerns a class of deferred correction methods recently developed for initial value ordinary differential equations; such methods are based on a Picard integral form of the correction equation. These methods divide a given timestep [t_n,t_n+1] into substeps, and use function values computed at these substeps to approximate the Picard integral by means of a numerical quadrature. The main purpose of this paper is to present a detailed analysis of the implications of the location of quadrature nodes on the accuracy and stability of the overall method. Comparisons between Gauss-Legendre, Gauss-Lobatto, Gauss-Radau, and uniformly spaced points are presented. Also, for a given set of quadrature nodes, quadrature rules may be formulated that include or exclude function values computed at the left-hand endpoint t_n. Quadrature rules that do not depend on the left-hand endpoint (which are referred to as right-hand quadrature rules) are shown to lead to L(α)-stable implicit methods with α≈π/2. The semi-implicit analog of this property is also discussed. Numerical results suggest that the use of uniform quadrature nodes, as opposed to nodes based on Gaussian quadratures, does not significantly affect the stability or accuracy of these methods for orders less than ten. In contrast, a study of the reduction of order for stiff equations shows that when uniform quadrature nodes are used in conjunction with a right-hand quadrature rule, the form and extent of order-reduction changes considerably. Specifically, a reduction of order to is observed for uniform nodes as opposed to for non-uniform nodes, where Δt denotes the time step and ε a stiffness parameter such that ε→0 corresponds to the problem becoming increasingly stiff. AMS subject classification (2000) 65B05     

投资的收益和风险的数学模型及算法研究

本文按照“满意解”、“多组解”的思路对投资的收益和风险问题进行了分析和处理 ,提出了将净收益与总体风险划分为若干等级 ,并按等级求出多组满意解的思想方法 ,最后对模型的数学性质与计算方法进行了初步研究