高阶导数切触有理插值算法

已有关于高阶导数有理插值方法的研究大都是基于广义范德蒙逆矩阵的思想,计算复杂度较高.本文利用埃米特插值基函数的方法和多项式插值的误差性质,给出一种满足高阶导数插值条件的切触有理插值算法,并且适用于向量值切触有理插值及插值重度不相等的情形,解决切触有理插值函数的存在性及算法复杂性问题.较之其他算法,具有计算复杂度较低,便于实际应用等特点.最后通过数值例子说明该算法的有效性.     

Multiquadric拟插值对高阶导数逼近的稳定性分析 谨以此文致《中国科学》创刊六十周年

基于样本数据来数值模拟函数的高阶导数是数值逼近中遇到的一类重要而且基本的问题,差商方法是数值微分的传统方法.但是在实际问题的求解中,它表现出强烈的不稳定性.在实际应用中,由于差商计算的不稳定性,它仅能用来模拟函数的低阶导数.为了更好地模拟函数的高阶导数,本文利用multiquadric拟插值提出了一种新的方法.并将multiquadric拟插值方法模拟函数导数的稳定性与传统差商方法所得结果进行了对比.数值例子很好地验证了本文的理论.从理论论证和数值例子比较来看,multiquadric拟插值方法比差商方法更为稳定.这个性质也表明,基于散乱甚至有干扰的数据,在逼近函数的高阶导数时,multiquadric拟插值方法是一个有效的工具.     

Multiquadric 拟插值对高阶导数逼近的稳定性分析

基于样本数据来数值模拟函数的高阶导数是数值逼近中遇到的一类重要而且基本的问题, 差商方法是数值微分的传统方法. 但是在实际问题的求解中, 它表现出强烈的不稳定性. 在实际应用中, 由于差商计算的不稳定性, 它仅能用来模拟函数的低阶导数. 为了更好地模拟函数的高阶导数, 本文利用multiquadric 拟插值提出了一种新的方法. 并将multiquadric 拟插值方法模拟函数导数的稳定性与传统差商方法所得结果进行了对比. 数值例子很好地验证了本文的理论. 从理论论证和数值例子比较来看, multiquadric 拟插值方法比差商方法更为稳定. 这个性质也表明, 基于散乱甚至有干扰的数据, 在逼近函数的高阶导数时, multiquadric 拟插值方法是一个有效的工具.     

曲边三角形域上具有高代数精确度的边界插值公式

1 曲边三角形上的边界插值公式 P.Barhill,G.Birkhoff,W.J.Gordon,梁学章等在[1]—[6]中已经得到一系列有用的具有一次、二次代数精确度的边界插值公式,但是,上述所有的工作其插值区域均     

非结构网格上求解二维H-J方程的一种WENO格式

基于WENO(Weighted Essentially Non-Oscillatory)的思想,提出了一种在非结构网格上求解二维Hamilton-Jacobi(简称H-J)方程的数值方法.该方法利用Abgrall提出的数值通量,在每个三角形单元上构造三次加权插值多项式,得到了一个求解H-J方程的高阶精度格式.数值实验结果表明,该方法计算速度较快,具有较高的精度,而且对导数间断有较高的分辨率.     

切触有理插值函数的新算法

切触有理插值函数的算法大都是基于连分式进行的,其算法的可行性大都是有条件的,且有理函数次数较高,计算量较大.文章利用拉格朗日插值的性质和分段组合的方法,给出了一种新的切触有理插值算法,并给出误差估计且将其推广到向量值切触有理插值情形.较之其他算法,具有有理函数次数较低、计算量较小、算法无条件性、无极点、满足高阶导数插值条件等优点.     

典型域上高阶Frchet导数的Schwarz-Pick估计

本文给出了典型域上带正实部的全纯函数高阶Frchet导数的Schwarz-Pick估计.推广了单位圆盘和单位球上带正实部的全纯函数高阶偏导数的Schwarz-Pick估计.     

典型域上高阶Fréechet导数的Schwarz-Pick估计

本文给出了典型域上带正实部的全纯函数高阶Fr¶echet 导数的Schwarz-Pick 估计. 推广了单位圆盘和单位球上带正实部的全纯函数高阶偏导数的Schwarz-Pick 估计.     

论Hermite插值

本文给出了Hermite插值多项式及其各阶导数的显式表示. 对于一个在x的某个领域内有足够高阶连续导数的函数f和位于该领域的任意一组节点, 给出了用f的Hermite插值多项式在点x的任意阶导数逼近f(x)的相应导数时余项的渐近表示.     

基于Beta函数及其偏导数的广义积分的高精度快速计算

考虑Beta函数偏导数的计算以及与此相关的广义积分的高精度快速计算问题.首先将Beta函数B(x,y)的定义扩展到整个复平面上,并建立了在整个复平面上Beta函数B(x,y)的偏导数的递推公式.对许多广义积分我们给出Beta函数偏导数的表示形式,因而利用Beta函数的偏导数计算这些广义积分.数值计算表明,算法无论从计算精度还是计算速度,远好于数值积分.另外,得到了B_(p,q)(x,y)存在闭形式的条件,并给出一些广义积分的闭形式.     

A domain decomposition and mixed method for a linear parabolic boundary value problem

In this paper, we discuss the convergence of a domain decompositionmethod for the solution of linear parabolic equations in theirmixed formulations. The subdomain meshes need not be quasi-uniform;they are composed of triangles or quadrilaterals that do notmatch at interfaces. For the ease of computation, this lackof continuity is compensated by a mortar technique based onpiecewise constant (discontinuous) multipliers. It is shownthat the method on triangles, parallelograms or slightly distortedparallelograms is convergent at the expense of a half-orderloss of accuracy compared with mortar methods based on piecewiselinear multipliers.     

Pseudospectral method for quadrilaterals

In this paper, we investigate the pseudospectral method on quadrilaterals. Some results on Legendre-Gauss-type interpolation are established, which play important roles in the pseudospectral method for partial differential equations defined on quadrilaterals. As examples of applications, we propose pseudospectral methods for two model problems and prove their spectral accuracy in space. Numerical results demonstrate the efficiency of the suggested algorithms. The approximation results and techniques developed in this paper are also applicable to other problems defined on quadrilaterals.     

Homothetic transformations and geometric loci: properties of triangles and quadrilaterals

In this paper, we use geometric transformations to find some interesting properties related with geometric loci. In particular, given a triangle or a cyclic quadrilateral, the locus generated by the centroid or by the orthocentre (for triangles) or by the anticentre (for cyclic quadrilaterals) when one vertex moves on the circumcircle of the figure are considered. These loci are studied in paragraphs 3 and 4. By means of the homothetic transformations some properties of triangles and quadrilaterals are found. The study of these properties can be used, with profit, in a classroom activity supported by Dynamic Geometry System.     

Pseudospectral method for quadrilaterals

In this paper, we investigate the pseudospectral method on quadrilaterals. Some results on Legendre–Gauss-type interpolation are established, which play important roles in the pseudospectral method for partial differential equations defined on quadrilaterals. As examples of applications, we propose pseudospectral methods for two model problems and prove their spectral accuracy in space. Numerical results demonstrate the efficiency of the suggested algorithms. The approximation results and techniques developed in this paper are also applicable to other problems defined on quadrilaterals.     

边界为三角形或四边形时反平面弹性或Laplace方程中的退化尺寸问题

对于反平面弹性或Laplace方程的外部边值问题, 给出了三角形或四边形周界时一系列退化尺寸问题的解,并利用了Schwarz-Christoffel 保角映象．证实当某一尺寸“R”等于它的临界值或一个单位值时,一个形式上简明的复位函数满足单位圆上位移为0的条件,或w=0．这就意味着在实际平面上的退化尺寸已经得到．最后,退化尺寸可从某些特殊积分得出,这些积分依赖于保角映象中的诸参数．给出了三角形或四边形周界时一系列退化尺寸问题的数值结果．     

弹性波方程有限元模拟的曲边地表处理

本文对比研究了关于弹性波模拟中的曲边地表形状处理的两种方法,一种是用给定的实际介质数值划定的地表形状,另一种是用样条插值逼近地表形状.本文采用有限元方法进行弹性波数值模拟,给出了基于这两种方法计算的数值例子,并对结果进行了分析比较.结果表明使用后一种方法对地表进行处理时,地表人工离散产生的干扰明显减少,优于前一种方法.     

Steiner Trees on Curved Surfaces

 The Steiner tree problem on surfaces is more complicated than the corresponding one in the Euclidean plane. There are not many results on it to date. In this paper we first make a comparison of Steiner minimal trees on general curved surfaces with Steiner minimal trees in the Euclidean plane. Then, we focus our study on the Steiner trees on spheres. In particular, we detail the properties of locally minimal Steiner points, and the Steiner points for spherical triangles. Received: August 18, 1997 Final version received: March 16, 1998     

Approximation of quadrilaterals by rational quadrilaterals in the plane

Many questions about triangles and quadrilaterals with rational sides, diagonals and areas can be reduced to solving certain diophantine equations. We look at a number of such questions including the question of approximating arbitrary triangles and quadrilaterals by those with rational sides, diagonals and areas. We transform these problems into questions on the existence of infinitely many rational solutions on a two parameter family of quartic curves. This is further transformed to a two parameter family of elliptic curves to deduce our main result concerning density of points on a line which are at a rational distance from three collinear points (Theorem 4). We deduce from this a new proof of density of rational quadrilaterals in the space of all quadrilaterals (Theorem 39). The other main result (Theorem 3) of this article is on the density of rational triangles which is related to analyzing rational points on the unit circle. Interestingly, this enables us to deduce that parallelograms with rational sides and area are dense in the class of all parallelograms. We also give a criterion for density of certain sets in topological spaces using local product structure and prove the density Theorem 6 in the appendix section. An application of this proves the density of rational points as stated in Theorem 31.     

Algebraic-Geometry Foundation for Constructing Smooth Interpolants on Curved Sides Element

1.IntroductionThealgebraicgeometrytheoryplaysaveryimportantroleinmanyareas-Forex-ample,thefundamentaltheoreminthemultiwriatepolynomialillterpolationtheoryl8]isestablishedbymeansofBezout'8theorem,thefundamentaJtheoreticalframeofmultivariatesplinefunctionsisgeneratedbymeansofcompatiblecthfactormethodI8]whichisalsocloselyrelatedwithBezout'stheo.em[9].ThepiecewisesmoothfunctionskillisusedfrequentlyinCAGD,FECandscattereddatafitting,etc.Inusingtheskin,thesmoothinginterpolationschemeanditsexplic…     

Magic of centroids

In this paper, we show some properties of centroids of geometric figures, such as triangles, quadrilaterals and tetrahedra. In particular, we will prove the properties by means of geometric transformations and by introducing extensions of triangles and quadrilaterals, i.e. by adding one, two or three new vertices to the figure. The study of these properties can be used, with profit, in a classroom activity supported by a dynamic geometry system.