四边简支正交异性板双向压屈模态的确定及其临界载荷的显式表达式

Libove曾经证明[1],四边简支的正交异性板在双向压力下的屈曲模态沿x方向和y方向的半波数m和n这两者中必有一者为1.本文将给出m=1或n=1的条件,并确定n=1时m的取值,及m=1时n的取值.从而完全确定了四边简支正交异性板在双向压力下的屈曲模态,并给出了临界载荷的显式表达式.     

非均匀变厚度圆盘的定常热传导

本文采用阶梯折算法,求得了任意非均匀变厚度圆盘定常热传导问题的一般解.并通过算例,对阶梯折算法的误差进行了分析.结果表明,该方法对于求解各类变系数常微分方程是十分有效的.     

关于非线性初边值问题的奇摄动(Ⅱ)

本文研究一类拟线性双曲—抛物型方程,具有变动边界的初边值问题的奇摄动:在某些条件成立,且ε充分小时,此问题的解具有以退化问题充分光滑解为首项的广义渐近展开式(Van der Corput意义),它在充分光滑解存在的区域Q={(x,t)|l₀(t)≤x≤l₁(t),0≤t≤T}上一致有效.其边界层存在于t=0附近.本文是工作[3]～[5]的进一步发展.     

三维抛物型方程的一族高精度分支稳定显格式

构造了一族解三维抛物型方程的高精度显格式,其稳定性条件为r=Δt/Δx2=Δt/Δy2=Δt/Δz2<1/2,截断误差为O(Δt2+Δx4).     

三维热传导方程的一族两层显式格式

提出了一族三维热传导方程的两层显式差分格式,当截断误差阶为O(Δt+(Δx)2)时,稳定性条件为网格比r=Δt/(Δx)2=Δt/(Δy)2=Δt/(Δz)2≤1/2,优于其他显式差分格式。而当截断误差阶为O((Δt)2+(Δx)4)时,稳定性条件为r≤1/6,包含了已有的结果。     

非均匀变截面弹性圆环在任意载荷下的弯曲问题

本文在等刚度弹性圆环的初参数公式的基础上,利用[2]提出的阶梯折算法,进一步研究非均匀变截面弹性圆环的弯曲,得到了这类问题的通解,应当指出,这组通解对非均匀变截面圆柱拱的相应问题也是适用的.为验证所得的公式并说明这种方法的应用,文末给出了示例并进行了求解,圆环、圆拱是工程上经常采用的结构,它们的弯曲,Timoshenko,S.[5],Barber,J.R.[3],Roark,R J[4],津村利光[6]等曾作过很多研究.然而,迄今只求得了均匀材料、等截面圆环的通解。对变截面问题,仅仅求得了抗弯刚度是坐标的线性函数这一特殊情况的解.由于非均匀变截面问题常常导出变系数微分方程,它们的求解遇到很大的数学困难.本文通过阶梯折算法把非均匀变截面弹性圆环弯曲问题的变系数微分方程转化成一等效的等刚度圆环弯曲的常系数微分方程.为保证内力连续,引入虚拟内力,并以[1]导出的初参数公式为影响函数,通过积分构造出了非齐次解,从而求得了非均匀变截面弹性圆环弯曲问题的通解.     

非均匀弹性地基圆板轴对称弯曲的一般解

本文在阶梯折算法的基础上,提出一个新的方法——精确解析法,得到了非均匀弹性地基圆板弯曲的一般解.文中导出了在任意轴对称载荷和边界条件下求解非均匀弹性地基圆板和中心带孔圆板弯曲的一般公式,并给出一致收敛于精确解的证明.文中得到的一般解可直接计算无弹性地基圆板的弯曲问题.问题最后归结为求解一个二元一次代数方程.文末给出算例,算例表明无论内力和位移均可得到满意的结果.     

一类半线性椭圆型方程衰减正整解的存在唯一性

本文首先证明方程△u-m2u+f(x,u)=0,x∈Rn,n≥3,m>0存在衰减的正整解,然后重点证明这种解的唯一性。     

渐近法在一类强非线性系统中的应用

本文采用文[1、2]的渐近解形式,将渐近法推广到如下较为广泛一类的强非线性振动系统式中g和f为x,的非线性解析函数,ε>0为小参数,并假设对应于ε=0的派生系统有周期解.本文推得系统(0.1)的渐近解递推方法,并应用于实例.     

一个分段线性Hénon映射吸引集合的结构

本文采用对偶线映射的方法分析了分段线性Hénon映射(x,y)→(1-a|x|+by,x),a=8/5,b=9/25吸引集的详细结构.设A和B分别是映射在第一和第三象限内的不动鞍点,本文说明:(1)映射的吸引集是B的不稳定流形U_B的闭包ū_B,而A的不稳定流形U_A则是ū_B的一个子集;(2)吸引盆是A的稳定流形S_A的闭包S_A,其边界是B的稳定流形S_B,而S_B在A_A的极限集之内.文中还给出周期鞍点不稳定流形和不动鞍点不稳定流形之间的关系.文中的符号动力学记号可用以研究各个不变流形每段的动态以及各同宿点、异宿点的动态.     

Constructing simple residuated lattices

A method of constructing residuated lattices is presented. As an application, examples of simple, integral, cancellative, distributive residuated lattices are given that are not linearly ordered. This settles a problem raised in [5] and [2].     

对矩阵初等变换应用中某些问题的探讨

运用初等变换的正确步骤可以减少计算量,现行用初等变换求向量组的一个极大无关组的两种方法,各有所长,文[5]的批评是不全面的.     

Dealing with linear dependence during the iterations of the restarted block Lanczos methods

The Lanczos method can be generalized to block form to compute multiple eigenvalues without the need of any deflation techniques. The block Lanczos method reduces a general sparse symmetric matrix to a block tridiagonal matrix via a Gram–Schmidt process. During the iterations of the block Lanczos method an off-diagonal block of the block tridiagonal matrix may become singular, implying that the new set of Lanczos vectors are linearly dependent on the previously generated vectors. Unlike the single vector Lanczos method, this occurrence of linearly dependent vectors may not imply an invariant subspace has been computed. This difficulty of a singular off-diagonal block is easily overcome in non-restarted block Lanczos methods, see [12,30]. The same schemes applied in non-restarted block Lanczos methods can also be applied in restarted block Lanczos methods. This allows the largest possible subspace to be built before restarting. However, in some cases a modification of the restart vectors is required or a singular block will continue to reoccur. In this paper we examine the different schemes mentioned in [12,30] for overcoming a singular block for the restarted block Lanczos methods, namely the restarted method reported in [12] and the Implicitly Restarted Block Lanczos (IRBL) method developed by Baglama et al. [3]. Numerical examples are presented to illustrate the different strategies discussed.     

A factorization method for the solution of constrained linear least squares problems allowing subsequent data changes

Summary In this paper we describe how to use Gram-Schmidt factorizations of Daniel et al. [1] to realize the method of [8] for solving linearly constrained linear least squares problems. The main advantage of using these factorizations is that it is relatively easy to take data changes into account, if necessary.The algorithm is compared numerically with two other codes, one of them published by Lawson and Hanson [3]. Further computational tests show the efficiency of the proposed methods, if a few data of the original problem are changed subsequently.This paper was sponsored by Deutsche Forschungsgemeinschaft, Bonn-Bad Godesberg     

A MODIFIED VARIABLE-PENALTY ALTERNATING DIRECTIONS METHOD FOR MONOTONE VARIATIONAL INEQUALITIES

Alternating directions method is one of the approaches for solving linearly constrained separate monotone variational inequalities. Experience on applications has shown that the number of iteration significantly depends on the penalty for the system of linearly constrained equations and therefore the method with variable penalties is advantageous in practice. In this paper, we extend the Kontogiorgis and Meyer method [12] by removing the monotonicity assumption on the variable penalty matrices. Moreover, we introduce a self-adaptive rule that leads the method to be more efficient and insensitive for various initial penalties. Numerical results for a class of Fermat-Weber problems show that the modified method and its self-adaptive technique are proper and necessary in practice.     

Sharp energy estimates for nonlinearly locally damped PDEs via observability for the associated undamped system

We consider the problem of sharp energy decay rates for nonlinearly damped abstract infinite-dimensional systems. Direct methods for nonlinear stabilization generally rely on multiplier techniques, and thus are valid under restrictive geometric conditions compared to the optimal geometric optics condition of Bardos et al. (1992) [10]. We prove sharp, simple and quasi-optimal energy decay rates through an indirect method, namely an observability estimate for the corresponding undamped system. One of the main advantage of these results is that they allow to combine optimal geometric conditions, as for instance that of Bardos et al. (1992) [10] and the optimal-weight convexity method of the first author (Alabau-Boussouira, 2010 [6], Alabau-Boussouira, 2005 [2]) to deduce very simple and quasi-optimal energy decay rates for nonlinearly locally damped systems. We also show that using arguments based on Russell's principle (Russell, 1978 [24]), one can deduce sharp energy decay rates from the exponential stabilization of the linearly damped system. Our results extend to nonlinearly damped systems, those of Haraux (1989) [14] and Ammari and Tucsnak (2001) [9] which concern linearly damped systems.     

Further Developments in an Iterative Projection and Contraction Method for Linear Programming

A linear programming problem can be translated into an equivalent general linear complementarity problem, which can be solved by an iterative projection and contraction (PC) method [6]. The PC method requires only two matrix-vector multiplications at each iteration and the efficiency in practice usually depends on the sparsity of the constraint-matrix. The prime PC algorithm in [6] is globally convergent; however, no statement can be made about the rate of convergence. Although a variant of the PC algorithm with constant step-size for linear programming [7] has a linear speed of convergence, it converges much slower in practice than the prime method [6]. In this paper, we develop a new step-size rule for the PC algorithm for linear programming such that the resulting algorithm is globally linearly convergent. We present some numerical experiments to indicate that it also works better in practice than the prime algorithm.     

Lexicographic Products of Half Linearly Ordered Groups

The notion of the half linearly ordered group (and, more generally, of the half lattice ordered group) was introduced by Giraudet and Lucas [2]. In the present paper we define the lexicographic product of half linearly ordered groups. This definition includes as a particular case the lexicographic product of linearly ordered groups. We investigate the problem of the existence of isomorphic refinements of two lexicographic product decompositions of a half linearly ordered group. The analogous problem for linearly ordered groups was dealt with by Maltsev [5]; his result was generalized by Fuchs [1] and the author [3]. The isomorphic refinements of small direct product decompositions of half lattice ordered groups were studied in [4].     

Resolving degeneracy in quadratic programming

A technique for the resolution of degeneracy in an Active Set Method for Quadratic Programming is described. The approach generalises Fletcher's method [2] which applies to the LP case. The method is described in terms of an LCP tableau, which is seen to provide useful insights. It is shown that the degeneracy procedure only needs to operate when the degenerate constraints are linearly dependent on those in the active set. No significant overheads are incurred by the degeneracy procedure. It is readily implemented in a null space format, and no complications in the matrix algebra are introduced.The guarantees of termination provided by [2], extending in particular to the case where round-off error is present, are preserved in the QP case. It is argued that the technique gives stronger guarantees than are available with other popular methods such as Wolfe's method [11] or the method of Goldfarb and Idnani [7].Presented at the 14th International Symposium on Mathematical Programming, Amsterdam, August 5–9, 1991.     

Existence of chaos in evolution equations

For a general evolution equation with a Silnikov homoclinic orbit, Smale horseshoes are constructed with the tools of [1] and in the same way as in [1]. The linear part of the evolution equation has a finite number of unstable modes. For evolution equations with infinitely many linearly unstable modes, the problem is still open.