阻尼系统重特征对导数的计算

提出了一种计算阻尼系统重特征值及其特征向量导数的方法．该方法利用n维空间的特征向量计算特征对的导数,避免了状态空间中特征向量的使用,从而节省了计算量,提高了计算效率．最后以一个5自由度的非比例阻尼系统对所提方法进行了数值试验,数值结果表明方法是有效的．     

二次特征值问题特征对的一阶与二阶偏导数

本文研究了解析依赖于多参数的二次特征值问题特征对偏导数的计算.利用计算广义特征值问题特征向量偏导数的模态法.提出了一种计算二次特征值问题特征对一阶、二阶偏导数的方法.本文最后以弹簧质点阻尼系统为例验证了所给结论的正确性和方法的有效性.     

计算二次特征值问题单特征三元组二阶偏导数的单模态法

本文提出了计算二次特征值问题单特征三元组的二阶偏导数的单模态法.该方法只需要用到待求二阶偏导数的特征三元组的信息;在计算特征向量二阶偏导数时只需求解一个线性方程组,该线性方程组的系数矩阵的阶数为n-1(n为二次特征值问题的规模),且系数矩阵的条件数恰好为其最大与最小非零奇异值的比值.本文给出三个例子进行了数值试验,并与...     

计算Riemann-Liouville分数阶积分和导数的数值算法

研究计算Riemann-Liouville (RL)分数阶积分和导数的数值算法.首先,分析了RL分数阶积分和导数的定义式,由于定义式中包含一个积分瑕点,使RL分数阶积分和导数难于计算.然后,给出了一种去掉积分瑕点的方法,在此基础上设计出计算RL分数阶积分和导数的数值算法,并证明了此数值算法具有一阶精度.最后,给出了计算实例,计算结果说明提出的算法是有效的.     

复特征值的一阶摄动解

本文将矩阵摄动法,推广到系统质量、阻尼和刚度矩阵为非对称的情形,引入伴随特征向量的概念,应用复模态理论中的正交关系,导出了系统复特征值的一阶摄动解。数值算例表明,这一方法是可行有效的。     

Gauss白噪声激励下分数阶导数系统的非平稳响应

研究了Gauss(高斯)白噪声激励下具有分数阶导数阻尼的非线性随机动力系统的非平稳响应.应用等价线性化方法将非线性系统转化为等价的线性系统,之后采用随机平均法获得系统响应满足的FPK(Fokker-Planck-Kolmogorov)方程,其中分数阶导数近似为一个周期函数.使用Galerkin方法求解FPK方程进而得到系统的近似非平稳响应.数值结果验证了方法的正确性和有效性.     

计算函数导数的FODF-SPH方法

在光滑粒子流体动力学(Smooth Particle Hydrodynamics:SPH)核近似方法原理的基础上,通过泰勒级数展开提出了计算函数导数的新FODF-SPH(Frist Order Derivative Free:FODF)方法,并分别推导一维、二维及三维情况下,计算函数的导数核估计的离散形式.用不同的粒子间距和不同的光滑长度计算一维和二维函数导数,与传统SPH方法进行误差对比分析.结果表明,与传统方法对比提出的计算方法的误差小、收敛速度快且计算过程避免核函数导数计算等优越性,因此在工程应用和数值计算中具有较强的适用范围.     

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.     

数值求解最优控制问题中的精确导数计算方法

针对常微分方程最优控制问题的数值求解,提出了一种自动计算性能指标梯度的方法.该方法通过显式数值积分方法求解状态方程,将最优控制的性能指标看作控制参数向量的显式函数,并根据链式求导法则计算其梯度.针对欧拉法和四阶龙格库塔法,推导了下一时刻状态对当前状态及控制导数的解析表达式.在求解状态方程的过程中,计算并采用行压缩方式存储了这些数值.然后在计算性能指标时反向计算,获得性能指标的精确梯度,并将其用于基于梯度的最优控制求解.通过计算实例验证了所计算导数的准确性,并在求解最优控制问题时与前向差分梯度方法进行了比较,求解结果表明了该方法的有效性.     

一类非对称各向同性张量函数导数的不变表示

将Dui和Chen于2004年提出的求解对称各向同性张量函数导数的方法推广到一类满足可交换条件的非对称各向同性张量函数情况,此类函数比以往研究的更具一般性．在有3个不同特征根时,由可交换性引进张量函数相对应的标量函数,进而求得此类非对称各向同性张量函数及其导数的不变表示形式．在2或3重特征根时,利用求极限的办法给出此类张量函数及其导数的表示形式．     

Multigrid algorithm from cyclic reduction for Markovian queueing networks

A multigrid method based on cyclic reduction strategy is proposed to solve huge, nonsymmetric singular linear systems arising from Markovian queueing networks. A simple way to construct the matrix-dependent prolongation and restriction operators is presented in this paper. Numerical results for multiple queues are given to illustrate the efficiency and robustness of our methods.     

Multigrid transfers for nonsymmetric systems based on Schur complements and Galerkin projections

A framework is proposed for constructing algebraic multigrid transfer operators suitable for nonsymmetric positive definite linear systems. This framework follows a Schur complement perspective as this is suitable for both symmetric and nonsymmetric systems. In particular, a connection between algebraic multigrid and approximate block factorizations is explored. This connection demonstrates that the convergence rate of a two‐level model multigrid iteration is completely governed by how well the coarse discretization approximates a Schur complement operator. The new grid transfer algorithm is then based on computing a Schur complement but restricting the solution space of the corresponding grid transfers in a Galerkin‐style so that a far less expensive approximation is obtained. The final algorithm corresponds to a Richardson‐type iteration that is used to improve a simple initial prolongator or a simple initial restrictor. Numerical results are presented illustrating the performance of the resulting algebraic multigrid method on highly nonsymmetric systems. Copyright © 2013 John Wiley & Sons, Ltd.     

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     

On nonlinear generalized conjugate gradient methods

Summary. The Generalized Conjugate Gradient method (see [1]) is an iterative method for nonsymmetric linear systems. We obtain generalizations of this method for nonlinear systems with nonsymmetric Jacobians. We prove global convergence results. Received April 29, 1992 / Revised version received November 18, 1993     

On the convergence behavior of the restarted GMRES algorithm for solving nonsymmetric linear systems

The solution of nonsymmetric systems of linear equations continues to be a difficult problem. A main algorithm for solving nonsymmetric problems is restarted GMRES. The algorithm is based on restarting full GMRES every s iterations, for some integer s>0. This paper considers the impact of the restart frequency s on the convergence and work requirements of the method. It is shown that a good choice of this parameter can lead to reduced solution time, while an improper choice may hinder or preclude convergence. An adaptive procedure is also presented for determining automatically when to restart. The results of numerical experiments are presented.     

粘性阻尼线性振动系统的复模态特征值问题的一种新的矩阵摄动分析解法

本文提出了对粘性阻尼线性振动系统的复模态二次广义特征值问题进行高效近似求解的一种新的矩阵摄动分析方法,即先将阻尼矩阵分解为比例阻尼部分和非比例阻尼部分之和,并求得系统的比例阻尼实模态特征解;然后以此为初始值,将阻尼矩阵的非比例部分作为对其比例部分的小量修改,利用摄动分析方法简捷地得到系统的复模态特征值问题的近似解.这一新方法适用于振系阻尼分布不十分偏离比例阻尼情况的问题,因此对大阻尼(非过阻尼)振动系统也有效.这是它优于以前提出的基于无阻尼实模态特征解的类似摄动分析方法的重要特点.文中建立了复模态特征值和特征向量的二阶摄动解式,并通过算例证实了其有效性.此外还讨论了利用比例阻尼假定估计阻尼系统固有振动的复特征值的可行性.     

Multigrid method for solving convection-diffusion problems with dominant convection

A modification of the multigrid method for the solution of linear algebraic equation systems with a strongly nonsymmetric matrix obtained after difference approximation of the convection-diffusion equation with dominant convection is proposed. Specially created triangular iterative methods have been used as the smoothers of the multigrid method. Some theoretical and numerical results are presented.     

Generalizations and modifications of the GMRES iterative method

For solving nonsymmetric linear systems, the well-known GMRES method is considered to be a stable method; however, the work per iteration increases as the number of iterations increases. We consider two new iterative methods GGMRES and MGMRES, which are a generalization and a modification of the GMRES method, respectively. Instead of using a minimization condition as in the derivation of GGMRES, we use a Galerkin condition to derive the MGMRES method. We also introduce another new iterative method, LAN/MGMRES, which is designed to combine the reliability of GMRES with the reduced work of a Lanczos-type method. A computer program has been written based on the use of the LAN/MGMRES algorithm for solving nonsymmetric linear systems arising from certain elliptic problems. Numerical tests are presented comparing this algorithm with some other commonly used iterative algorithms. These preliminary tests of the LAN/MGMRES algorithm show that it is comparable in terms of both the approximate number of iterations and the overall convergence behavior. This revised version was published online in June 2006 with corrections to the Cover Date.     

Generalized global conjugate gradient squared algorithm

In this paper, a generalized global conjugate gradient squared method for solving nonsymmetric linear systems with multiple right-hand sides is presented. The method can be derived by using products of two nearby global BiCG polynomials and formal orthogonal polynomials, of which global CGS and global BiCGSTAB are just particular cases. We also show to apply the method for solving the Sylvester matrix equation. Finally, numerical examples are given to illustrate the effectiveness of the proposed method.