Numerical Inversion of the Mellin Transform

A method is described for the numerical inversion of the Mellintransform, without reduction of the problem to the inversionof the Laplace transform. The expansion of the original function(t) in a series of orthogonal Laguerre functions is used andthe coefficients of this expansion are obtained by means ofa collocation on the real axis of the transformed plane. Theperformance of the method is illustrated by the inversion offive test functions.     

Radon变换反演问题的数值方法

利用Tchebycheff多项式和古典Radon变换反演公式,本文得到了Tchebycheff变换对,从而导出了数值反演结果．     

A New Numerical Method for the Inversion of the Laplace Transform

This paper presents a new numerical method for the inversionof the Laplace transform, where only real values of the transformare known. This method, based on the approximation of the transformby truncated series of orthogonal functions, related to theJacobi or Laguerre polynomials, avoids the loss of significantfigures inherent in earlier methods.     

基于直接数值积分的Laplace逆变换方法的比较研究

为了探讨各种数值积分方法,如梯形公式、Simpson法、Gauss积分方法和振荡函数积分方法等,在数值Laplace逆变换中的应用效果,本文进行了基于各种离散数值积分公式的Laplace逆变换方法的比较研究,涉及到24种方法,针对Davies和Martin的16个考题,给出了数值比较结果,得出了一些新的结论。     

On the Numerical Inversion of the Laplace Transform of a Discontinuous Original

A method for approximate numerical Laplace transform inversionis expounded and applied to a particular problem related totheoretical seismology, which has a discontinuous solution.An essential feature is that the representation of the solutionin terms of elementary discontinuous functions enables rapidconvergence to be obtained.     

一种基于小波尺度函数变换的Laplace反演方法

该文基于Ｄａｕｂｅｃｈｉｅｓ小波尺度函数变换建立了关于Ｌａｐｌａｃｅ变换的一种反演数值方法．通过对小波尺度函数的低带通谱特性的定性与定量讨论,给出了这一反演方法所得原像函数的适用域．结果发现：其区域大小随着小波尺度函数的分辨指标（ｒｅｓｏｌｕｔｉｏｎｌｅｖｅｌ）选取的升高而增大．最后,以颤振曲线、具有指数增长的复函数、和一维振动弦的初边值问题等为例,定量给出了其反演方法的数值结果．通过与相应的原像精确结果对比发现：在反演的有效区域内,其数值反演的原像几乎与精确的原像图象重合．这表明这一Ｌａｐｌａｃｅ反演数值方法是有效和可靠的．     

拉普拉斯反变换的计算

在工程以及其它应用领域中常遇到求拉普拉斯反变换的问题.本文将拉普拉斯变换与它在工程中应用相结合,详细介绍了计算拉普拉斯反变换的几种有趣且行之有效的方法.     

一个全局和局部的Metro Carlo电磁转换及计算

本文提出了一个全局和局部的Metro Carlo电磁转换方法,找到了电磁材料参数,提供了一种关于全局和局部的电磁转换计算方法。     

On the Inversion of the xfct Radon Transform

It has been recently shown by Fokas [ 1 - 3 ] and Novikov [ 4 ] that the spectral analysis of a particular partial differential equation yields the inversion formula for the problem of computerized emission tomography. In this paper, we show that a similar analysis can be made for the case of X‐ray fluorescence tomography.     

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。     

Numerical Computation of Galois Groups

The Galois/monodromy group of a family of geometric problems or equations is a subtle invariant that encodes the structure of the solutions. We give numerical methods to compute the Galois group and study it when it is not the full symmetric group. One algorithm computes generators, while the other studies its structure as a permutation group. We illustrate these algorithms with examples using a Macaulay2 package we are developing that relies upon Bertini to perform monodromy computations.     

连续切波变换反演公式的级数表示

我们主要研究连续切波变换反演公式的级数表示.首先引入两类由切波变换反演公式定义的无穷级数和有限级数,并研究了由Kittipoom等人介绍的切波生成空间,得到这个切波生成空间的一些重要性质.其次利用这些结果显示:对于这个切波生成空间,当采样密度趋于无穷时由我们定义的无穷级数按L~2-范数收敛于重构函数;对于可允许函数空间,当采样密度趋于无穷时由我们定义的有限级数按L~2-范数收敛于重构函数.     

Inversion of the Short-Time Fourier Transform Using Riemannian Sums

The inversion formula for the short-time Fourier transform is usually considered in the weak sense, or only for specific combinations of window functions and function spaces such as L₂ and modulation spaces. In the present note the Riemannian sums of the inverse short-time Fourier transform are investigated. Under some conditions on the window functions we prove that the Riemannian sums converge to f in the modulation spaces and inWiener amalgam norms, hence also in the L_p sense.     

Numerical Computation of Multivariate Normal Probabilities

Abstract

The numerical computation of a multivariate normal probability is often a difficult problem. This article describes a transformation that simplifies the problem and places it into a form that allows efficient calculation using standard numerical multiple integration algorithms. Test results are presented that compare implementations of two algorithms that use the transformation with currently available software.     

Classroom Note: Fourier Method for Laplace Transform Inversion

A method is described for inverting the Laplace transform. The performance of the Fourier method is illustrated by the inversion of the test functions available in the literature. Results are shown in the tables.     

Numerical Computation of Waves at High Frequencies by an Iterated WKB-Method

An integral operator is defined, which allows to solve the equation by Neumann series for sufficiently large k > 0. The kernel is constructed by a modification of the WKB-method. This kernel is so simple that the operator can be used effectively for numerical calculations. Numerical results are discussed.     

Inversion Formula for Shearlet Transform in Arbitrary Space Dimensions

In this article, we study the convergence of the inverse shearlet transform in arbitrary space dimensions. For every pair of admissible shearlets, we show that although the integral involved in the inversion formula from the continuous shearlet transform is convergent in the L² sense, it is not true in general whenever pointwise convergence is considered. We give some su?cient conditions for the pointwise convergence to hold. Moreover, for any pair of admissible shearlets we show that the Riemannian sums defined by the inverse shearlet transform are convergent to the original function as the sampling density tends to infinity.     

The Accurate Numerical Inversion of Laplace Transforms

Numerical inversion of almost arbitrary Laplace transforms,for any value of t, to any prescribed accuracy up to atleastthree-quarters of the computer precision, is effected by trapezoidalintegration along a special contour. The required number ofpoints depends on t, the accuracy, and the transform singularitypositions, and for moderate t is typically 11 for errors oforder 10^–6, 18 for order 10^–10, 35 for order 10^–20(withdouble precision working).     

On the Fast Fourier Transform Inversion of Probability Generating Functions

The fast Fourier transform can be used to invert z transforms(including probability generating functions), but this applicationhas received little attention or use. This correspondence makesa case for the FFT as a standard numerical tool in queuing andother statistical analyses in order to obtain probability densityfunctions quickly and easily. Round-off and aliasing errorsare discussed briefly for the queuing analyst without a signalprocessing background. Several variations are described whichextend the accuracy and the utility of the method.     

Reliable Numerical Computation in Civil Engineering

Civil engineering is a field – as are many other engineering sciences – where most of the methods used for solving optimization problems are based on experience and experiments, and models using local information, but drawn from global models. The present work outlines an interesting class of problems from this field, and initiates some possible ways to solve those problems utilizing the wide tool capabilities of interval arithmetic for error handling and interval branch-and-bound algorithms to solve the original or modified industrial models automating civil engineers' work. The investigations are in the first state but are promising both in a theoretical and in a practical sense.