《论数值修约》的补充——数值修约的误差

本文用补数定义论述了四舍五入的误差问题.并用图示法显示各修约规则的误差.     

线性回归系数的修约规则

线性回归系数的修约规则黄映辉（西安交通大学管理学院）线性回归根据存有相互关系的变量ｙ，ｘｔ的观测值来确定回归系数ａ和ｂｉ，从而建立线性回归方程。因为观测值ｙ和ｘｉ通常为近似数，所以由ｙ和ｘｉ计算而得的回归系数ａ和ｂｉ也必为近似数，其修约误差可由ｙ，ｘ...     

关于正交变换两种定义方式的研讨

指出由于当前正交变换两种定义方式并存以及其中的定义2违反了给概念下定义的规则,已经导致了一些对正交变换概念的错误理解.建议各教材统一采用本文定义1的方式定义正交变换.上述研讨与结果也可平行地移植到酉变换上去.     

直接用定义解题的几种主要方式

解题离不开定义,直接用定义解题有以下几种主要方式: 1．用定义中的运算规则如果一个定义给出了它所定义的对象的运算规则,那么在解决与这个定义相关问题时,可以用该定义中的运算规则来解决这个问题．例1已知f(x)=(x-a)n(n是正整数),     

关于《连对角占优矩阵的一些性质》的注记

本文指出[1]中一些结论是错误的,并说明产生错误的原因. 为了便于说明问题,我们采用文[1]中的定义和记号.首先将[1]中引理2叙述如下: 引理2 若A∈C~(m×n)为不可约矩阵,又假定A的一个特征值λ是卵形|z-a_(ii)||z-a_(jj)|≤Λ_iΛ_j的并集的一个边界点,则所有n(n-1)/2个卵形圆周|z-a_(ii)||x-a_(ii)|=Λ_iΛ_j(i≠i,i,j=?)都通过点.     

基于模糊错误逻辑的投资结构优化研究

主要研究模糊错误逻辑的运算,设定了模糊错误逻辑的基本运算规则,对模糊错误逻辑公式、变量、真值、函数、字、子句、字组等概念进行定义,在此基础上,提出2个定理并予以证明,揭示了模糊错误逻辑在错误的传递、转化与消除过程中的运算规律和性质 ,然后建立了优化投资结构模糊错误逻辑模型.     

带单向关闭和多种维修方式的两部件串联可修模型

本文讨论的带单向关闭规则和多种维修方式的两部件串联可修模型,比许多现有模型更一般。我们用向量马氏过程方法求得了它的可靠度和可用度,在(0,t)中的平均故障次数和平均更新次数。     

解波方程逆问题的时卷正则（TCR）迭代法的数值方法

本文提出了一种解波方程逆问题的莳卷正则(TCR)迭代方法[2]的数值方法,这种方法巧妙地用Tikhonov正则法克服了由于数值磨光所引起的不稳定性,使TCR迭代过程稳定收敛。同时本文还采用了某些多层网格迭代技巧,并提出了一个简单实用的选择正则参数的方法,从而提高了迭代收敛速度。此外,本文还指出这种数值方法可用于解非边界脉冲源的波方程逆问题。     

古今对照 发展学生数学公理化思想——以等腰三角形两底角相等为例

1引言《义务教育数学课程标准(2011年版)》指出:数学课程能培养学生的抽象思维和推理能力.推理包括合情推理和演绎推理,演绎推理是从已有的事实(包括定义、公理、定理等)和确定的规则(包括运算的定义、法则、顺序等)出发,按照逻辑推理的法则证明和计算[1].《普通高中数学课程标准(2017年版)》指出:逻辑推理是指从一些事实和命题出发,依据规则推出其他命题的素养.逻辑推理是得到数学结论、构建数学体系的重要方式,是数学严谨性的基本保证,是人们在数学活动中进行交流的基本思维品质[2].     

用区域分解法求不可压N-S方程的差分解

§1.引言 对不可压小粘性流的数值解,[1]和[2]用奇异摄动观点提出了一个区域分解法.从常微分方程(组)的奇异摄动问题出发,解分解为外部解加边界修正解(以下简称为修正解).外部解的边界条件有:给定(原边界条件)、待定(用原边界条件和修正解)和延拓类.修正解的边界条件有:给定(用原边界条件和外部解延拓)渐近(在边界层外缘)和待定     

Towards accurate statistical estimation of rounding errors in floating-point computations

A new method of estimatinga posteriori the statistical characteristics of the rounding errors of an arbitrary algorithm is presented. This method is based on a discrete model of the distribution of rounding errors which makes more accurate estimates possible. The analysis is given for both rounding and truncating arithmetic. Finally, some experimental results are reported.     

Forward error analysis of Gaussian elimination

Summary Part I of this work deals with the forward error analysis of Gaussian elimination for general linear algebraic systems. The error analysis is based on a linearization method which determines first order approximations of the absolute errors exactly. Superposition and cancellation of error effects, structure and sparsity of the coefficient matrices are completely taken into account by this method. The most important results of the paper are new condition numbers and associated optimal component-wise error and residual estimates for the solutions of linear algebraic systems under data perturbations and perturbations by rounding erros in the arithmetic floating-point operations. The estimates do not use vector or matrix norms. The relative data and rounding condition numbers as well as the associated backward and residual stability constants are scaling-invariant. The condition numbers can be computed approximately from the input data, the intermediate results, and the solution of the linear system. Numerical examples show that by these means realistic bounds of the errors and the residuals of approximate solutions can be obtained. Using the forward error analysis, also typical results of backward error analysis are deduced. Stability theorems and a priori error estimates for special classes of linear systems are proved in Part II of this work.     

Safe bounds in linear and mixed-integer linear programming

Current mixed-integer linear programming solvers are based on linear programming routines that use floating-point arithmetic. Occasionally, this leads to wrong solutions, even for problems where all coefficients and all solution components are small integers. An example is given where many state-of-the-art MILP solvers fail. It is then shown how, using directed rounding and interval arithmetic, cheap pre- and postprocessing of the linear programs arising in a branch-and-cut framework can guarantee that no solution is lost, at least for mixed-integer programs in which all variables can be bounded rigorously by bounds of reasonable size. Mathematics Subject Classification (2000):primary 90C11, secondary 65G20     

Analysis of some known methods of improving the accuracy of floating-point sums

Some well-known methods for calculating the round-off error in floating-point addition are analyzed in this paper. The methods have been introduced by Møller [16], Kahan [11] and Knuth [12]. The necessary and sufficient conditions under which these methods produce the value of the round-off error, for rounding, truncating and parity arithmetic, are given. The computer-oriented parity arithmetic is not commonly known, but it has some desirable properties, as this paper will demonstrate. Some experimental results are also reported.     

Software to support numerical analysis teaching

This paper describes a Fortran90 library designed to support the teaching of numerical analysis and its applications. As well as covering traditional material it introduces recent and important ideas in numerical computation such as interval arithmetic and automatic differentiation. The library rests on a module realpac which provides real arithmetic in a range of precisions with a choice of rounding strategies. This, in turn, supports the implementation of an interval arithmetic module intpac. Derived data types and overloaded operations help inexperienced users to interface with unfamiliar data types such as intervals. The library also includes more conventional modules such as lepac for solving linear systems and minpac for nonlinear optimization. These, however, can be enhanced by being linked to more sophisticated tools for sparse matrix handling and automatic differentiation. As well as showing the main structure and scope of the software, the paper mentions some exercises that have successfully been performed by students.     

Adaptive Precision Floating-Point Arithmetic and Fast Robust Geometric Predicates

Exact computer arithmetic has a variety of uses, including the robust implementation of geometric algorithms. This article has three purposes. The first is to offer fast software-level algorithms for exact addition and multiplication of arbitrary precision floating-point values. The second is to propose a technique for adaptive precision arithmetic that can often speed these algorithms when they are used to perform multiprecision calculations that do not always require exact arithmetic, but must satisfy some error bound. The third is to use these techniques to develop implementations of several common geometric calculations whose required degree of accuracy depends on their inputs. These robust geometric predicates are adaptive; their running time depends on the degree of uncertainty of the result, and is usually small. These algorithms work on computers whose floating-point arithmetic uses radix two and exact rounding, including machines complying with the IEEE 754 standard. The inputs to the predicates may be arbitrary single or double precision floating-point numbers. C code is publicly available for the two-dimensional and three-dimensional orientation and incircle tests, and robust Delaunay triangulation using these tests. Timings of the implementations demonstrate their effectiveness. Received May 16, 1996, and in revised form March 10, 1997.     

Rounding errors in numerical solutions of two linear equations in two unknowns

New condition numbers and stability constants for the numerical behaviour of Cramer's rule and Gaussian elimination for solving two linear equations in two unknowns under data perturbations and rounding errors of floating-point arithmetic are established. By these means fundamental error estimates and stability theorems are proved. The error estimates are illustrated by a series of numerical examples.     

An axiomatic approach to rounded computations

The present paper is intended to give an axiomatic approach to rounded computations. A rounding is defined as a monotone mapping of an ordered set into a subset, which in general is called a lower respectively an upper screen. The first chapter deals with roundings in ordered sets. In the second chapter further properties of roundings in linearly ordered sets are studied. The third chapter deals with the two most important applications, the approximation of the real arithmetic on a finite screen and the approximation of the real interval arithmetic on an upper screen. Beyond these examples various further applications are possible.Sponsored by the Mathematics Research Center, Madison, Wisconsin, under Contract No.: DA-31-124-ARO-D-462.     

Variants of the groupwise update strategy for short-recurrence Krylov subspace methods

Krylov subspace methods often use short-recurrences for updating approximations and the corresponding residuals. In the bi-conjugate gradient (Bi-CG) type methods, rounding errors arising from the matrix–vector multiplications used in the recursion formulas influence the convergence speed and the maximum attainable accuracy of the approximate solutions. The strategy of a groupwise update has been proposed for improving the convergence of the Bi-CG type methods in finite-precision arithmetic. In the present paper, we analyze the influence of rounding errors on the convergence properties when using alternative recursion formulas, such as those used in the bi-conjugate residual (Bi-CR) method, which are different from those used in the Bi-CG type methods. We also propose variants of a groupwise update strategy for improving the convergence speed and the accuracy of the approximate solutions. Numerical experiments demonstrate the effectiveness of the proposed method.