关于正定可对称化线性代数方程组的预对称正则化算法

1引言考虑线性代数方程组A_x=b,A∈R~(n×n)非奇异,x,b∈R~n(1)的求解．当系数矩阵是大型稀疏的正定可对称化矩阵,文[1,2]讨论了一类预对称共轭梯度算法(LRSCG算法是其中之一),这类算法的实质是利用非对称的系数矩阵可对称化的性质,并结合共轭梯度法而构造的一种预处理的共轭梯度法[12,16,17]．但非对称的系数     

参量离散代数Riccati方程对称解的两类迭代算法

基于求线性矩阵方程约束解的修正共轭梯度法,针对源于低增益反馈设计和时滞控制系统中的一类参量离散代数Riccati方程,建立求其非零对称解的Newton-MCG算法和非精确Newton-MCG算法以及求其可逆对称解的T-MCG算法.(非精确)Newton-MCG算法仅要求Riccati方程存在非零对称解,对系数矩阵等没有附加限定,但所得对称解不能保证可逆性或正定性;在系数矩阵满足可控性等条件下,由T-MCG算法所得对称解是正定的.数值算例表明,两类迭代算法是有效的.     

关于实方阵的几个问题

本文讨论如下内容：１．把有关对称正定（半正定）的一些性质推广到广义正定（半正定）。２．给定ｘ∈Ｒｍ×ｍ，∧为对角阵，求ＡＸ＝ｘ∧在对称半正定矩阵类中解存在的充要条件及一般形式，并讨论了对任意给定的对称正定（半正定）矩阵Ａ，在上述解的集合中求得Ａ，使得     

对称递减对角占优阵

本文提出对称递减对角占优阵和亚对称递减对角占优阵的概念,给出它们的一种实现阵的构造方法,指出这类Fuzzy阵的容度不大于它的阶数。     

参量连续代数Riccati方程对称解的两种迭代算法

基于求线性矩阵方程约束解的修正共轭梯度法,针对源于低增益反馈设计中的一类参量连续代数Riccati方程,建立求其非零对称解的两种互为补充的迭代算法,称之为变换-MCG算法和牛顿-MCG算法.在一定条件下,当Riccati方程存在可逆对称解或唯一对称正定解时,由变换-MCG算法所得对称解具备可逆性或正定性.牛顿-MCG算法仅要求Riccati方程存在非零对称解,对系数矩阵等没有附加限定,但所得对称解不能保证可逆性或正定性.数值算例表明,两种迭代算法是有效的.     

子空间上的对称正定及对称半正定阵的左右特征值反问题

文[1][2][3]中讨论AX＝B的对称阵逆特征值问题，文[4][5][6]中讨论了半正定阵的逆特征值问题。本文讨论了空间了子空间上的对称正定及对称半正定阵的左右特征值反问题，给出了解存在的充分条件及解的表达式。     

对称不定系统的一类预处理子的注记

由于对称正定系统已有很多有效的求解方法,因此将对称的、或者非对称的不定系统转化为对称正定系统就成为解决这类问题的方法之一构造了一类简洁有效的预处理子,将对称不定系统转化为对称正定型,研究了所得预处理系统的谱性质,估计了其谱条件数,推广了现有结论.     

两类四元数矩阵偶的GH合同标准形

该文给出两类四元数矩阵偶〈A，B１〉与〈A，B２〉的ＧＨ 合同标准形，其中A为半正定自共轭阵，B１ 为斜自共轭阵，B２ 为自共轭阵．由此分别得到（广义）半正定与正定四元数矩阵的ＧＨ合同标准形，以及矩阵同时对角化问题的若干个结果．     

二维椭圆型方程反问题中优化算法的比较

近年来，决定椭圆型方程系数反问题在地磁、地球物理、冶金和生物等实际问题上有着广泛的应用．本文讨论了二维的决定椭圆型方程系数反问题的数值求解方法．由误差平方和最小原则，这个反问题可化为一个变分问题，并进一步离散化为一个最优化问题，其目标函数依赖于要决定的方程系数．本文着重考察非线性共轭梯度法在此最优化问题数值计算中的表现，并与拟牛顿法作为对比．为了提高算法的效率我们适当选择加快收敛速度的预处理矩阵．同时还考察了线搜索方法的不同对优化算法的影响．数值实验的结果表明，非线性共轭梯度法在这类大规模优化问题中相对于拟牛顿法更有效．     

四元数体上重行列式的性质及其应用

本文得到了四元数体上重行列式的一些基本不等式，给出了矩阵为正定自共轭阵时，行列式与重行列式的显式关系，同时也给出了文［１］中行列式与文［５］中行列式两种定义的关系。提出了四元数体上广义正定自共轭阵的概念，并获得了这类阵的基本性质．     

Nonsymmetric systems on nonsmooth planar domains

We study boundary value problems, in the sense of Dahlberg, for second order constant coefficient strongly elliptic systems. In this class are systems without a variational formulation, viz. the nonsymmetric systems. Various similarities and differences between this subclass and the symmetrizable systems are examined in nonsmooth domains.

     

The modified extended Fan sub-equation method and its application to the (2+1)-dimensional Broer–Kaup–Kupershmidt equation

By using the Chen et al. ansatz [Chen Y, Wang Q, Lang Y. Naturforsch 2005;60a:127] and by modifying our extended Fan sub-equation method [Yomba E. Phys Lett A 2005;336:463]. We have obtained new and more general solutions including a series of non-travelling wave and coefficient function solutions namely: soliton-like solutions, triangular-like solutions, single and combined non-degenerate Jacobi elliptic wave function-like solutions for the (2+1)-dimensional Broer–Kaup–Kupershmidt equation. The most important achievement of this method lies on the fact that we have succeeded in one move to give all the solutions which can previously be obtained by application of at least four methods (the method using the Riccati equation, or the first kind elliptic equation, or the auxiliary ordinary equation, or the generalized Riccati equation as mapping equation).     

Solvability of the Tricomi problem for second order equations of mixed type with degenerate curve on the sides of an angle

In [1]–[6], the author posed and discussed the Tricomi problem of second order mixed equations, but he only consider some special mixed equations. In [3], the author discussed the uniqueness of solutions of the Tricomi problem for some second order mixed equation with nonsmooth degenerate line. The present paper deals with the Tricomi problem for general second order mixed equations with degenerate curve on the sides of an angle. I first give the formulation of the above problem, and then prove the solvability of the Tricomi problem for the mixed equations with degenerate curve on the sides of an angle, by using the existence of solutions of the mixed problem for the degenerate elliptic equations (see [11]). Here I mention that the used method in this paper is different to those in other papers or books, because I introduce the new notation (2.1) below, such that the second order equation of mixed type can be reduced to the first order complex equation of mixed type with singular coefficients, hence I can use the advantage of complex analytic method. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A new periodic solution to Jacobi elliptic functions of MKdV equation and BBM equation

Based on the homogeneous balance method,the Jacobi elliptic expansion method and the auxiliary equation method,the first elliptic function equation is used to get a new kind of solutions of nonlinear evolution equations.New exact solutions to the Jacobi elliptic function of MKdV equations and Benjamin-Bona-Mahoney (BBM) equations are obtained with the aid of computer algebraic system Maple.The method is also valid for other (1+1)-dimensional and higher dimensional systems.     

两不同部件串联可修系统的可用度的一个新的计算方法

本用直接解一组不含时间t的一阶线性偏微分积方程而得到两不同部件可修系统的可用度。     

有限元解的梯度佳点

我们考虑二阶椭圆方程的第一边值问题及奇妙族矩形元。文[2,3,9]证明了有限元解的梯度在高斯点具有超收敛性。本文假定椭圆方程的系数在有界区域Ω中曲线S上有第一类间断,在此意义下推广了文[2,3,9]。     

Hölder continuity of solutions of elliptic systems

The purpose of this note is to observe that a variant of the method of Morrey, as exposed in [4] and [5], can be used to show that weak solutions of a certain class of elliptic systems of quasilinear equations of arbitrary order of the form $$\mathop {\sum\limits_{\left| \alpha \right| \leqslant m} {( - 1)^{\left| \alpha \right|} D^\alpha F_{\alpha ,v} (x,u,Du, \ldots ,D^m u) = 0,v = 1,2 \ldots ,N} }\limits_{u = (u_1 ,u_2 , \ldots ,u_{N)} } $$ are Hölder continuous, thus partially extending results of Lady?enskaja-Ural'ceva [3] and Serrin [8] to higher order equations. A full extension is not possible. With suitable assumptions the Hölder continuity holds out to the boundary.     

On a nonlinear system consisting of three different types of differential equations

We consider a system consisting of a first order differential equation, a parabolic and an elliptic equation. Existence of weak solutions is proved by using the Schauder fixed point theorem. The paper improves some results of [3, 6] which is illustrated by example     

Potential bounds in problems on quasilinear elliptic equations

We study quasilinear elliptic equations with strong nonlinear terms and systems of such equations. The methods developed by the authors in [1], [2] are used to prove the existence of solutions for boundary—value problems using some information on behavior of potential bounds for nonlinearities; the L–characteristics of elliptic operators and their fractional powers play an important role. New conditions are suggested for the existence of classical solutions of quasilinear second order elliptic equations.     

Stable Asymptotics for Elliptic Systems on Plane Domains with Corners

We consider boundary value problems for elliptic systems in the sense of Agmon-Douglis-Nirenberg on plane domains with corners, where the domain, the coefficients of the operators and the right hand sides all depend on a parameter. We construct corner singularities in such a way that the corresponding decomposition of the solution into regular and singular parts is stable, i. e. the regular part and the coefficient of the singular functions depend smoothly on the parameter. The construction of these singular functions continues the paper [3] and generalizes results known for second order scalar boundary value problems — see [4,5] [12].