非线性发展型方程的Legendre拟谱逼近

本文考虑非稳态Burgers方程的拟谱逼近，构造了一类Legendre拟谱计算格式并证明了其收敛性，数值结果显示了格式的有效性。     

非线性互补问题的逐次逼近类Broyden算法

In this paper, we present a new form of successive approximation Broyden-like algorithm for nonlinear complementarity problem based on its equivalent nonsmooth equations. Under suitable conditions, we get the global convergence on the algorithms. Some numerical results are also reported.     

Approximation Methods for Inverse Problems Governed by Nonlinear Parabolic Systems

We present a rigorous theoretical framework for approximation of nonlinear parabolic systems with delays in the context of inverse least squares problems. Convergence of approximate optimal parameters and that of forward solutions in the context of semidiscrete Galerkin schemes are given. Sample numerical results demonstrating the convergence are given for a model of dioxin uptake and elimination in a distributed liver model that is a special case of the general theoretical framework.     

非线性问题转向点的数值予测

本文讨论了一类非线性问题及其有限元逼近问题的转向点之数值予测,以及应用于定常的Navier-Stokes问题.     

求解非线性互补问题的逐次逼近阻尼牛顿法

针对非线性互补问题,提出了与其等价的非光滑方程的逐次逼近阻尼牛顿法,并 在一定条件下证明了该算法的全局收敛性.数值结果表明,这一算法是有效的.     

A Critical Points Theorem and Nonlinear Differential Problems

The existence of two intervals of positive real parameters λ for which the functional Φ + λΨ has three critical points, whose norms are uniformly bounded in respect to λ belonging to one of the two intervals, is established. As an example of an application to nonlinear differential problems, a two point boundary value problem is considered and multiplicity results are obtained.     

局部凸I-拓扑线性空间的投影拓扑与投影极限

给出模糊线性序同态的某些性质. 在此基础上, 利用Katsaras意义下的局部凸I-拓扑线性空间概念的一个等价刻画, 引进并研究了新的投影拓扑与投影极限, 得到了与经典拓扑线性空间理论中相应定理相平行的结果, 改进和推广了严从华的结论.     

Gaussian Limit for Projective Characters of Large Symmetric Groups

In 1993, S. Kerov obtained a central limit theorem for the Plancherel measure on Young diagrams. The Plancherel measure is a natural probability measure on the set of irreducible characters of the symmetric group S _n. Kerov's theorem states that, as n, the values of irreducible characters at simple cycles, appropriately normalized and considered as random variables, are asymptotically independent and converge to Gaussian random variables. In the present work we obtain an analog of this theorem for projective representations of the symmetric group. Bibliography: 27 titles.     

关于非线性特征值多点边值问题的四个正解的存在性

利用锥上的不动点定理,考察了一类非线性特征值问题u″(t)+λf(t,u(t))=0,0≤t≤1,u(0)=0,αu(η)=u(1)的多个正解的存在性,给出了四个正解存在的充分条件,这里0<η<1,α>0.     

求解非线性互补问题的逐次逼近拟牛顿法的收敛性分析

提出了求解非线性互补问题的一个逐次逼近拟牛顿算法。在适当的假设下,证明了该算法的全局收敛性和局部超线性收敛性。     

一类非线性抛物最优控制问题的有限元误差估计

该文对一类非线性抛物最优控制问题给出了有限元逼近格式,并讨论了两种不同类型的控制约束集.文中对状态和伴随状态变量采用了线性连续函数离散,而控制变量则由分片常函数近似.得到了控制和状态逼近的先验误差估计■(h_U+h+k),这里h_U与h分别表示控制和状态的空间网格步长,k表示时间步长.数值试验表明了算法的有效性.     

具有转向点的非线性系统边值问题的奇摄动

本文应用微分不等式的方法,研究具有转向点的非线性系统两点边值问题的奇摄动.证明了当ε→0~ 时,其解的渐近性态.     

Double Positive Solutions of Fourth-Order Nonlinear Boundary Value Problems

We study boundary value problems for fourth-order ordinary differential equation of the form by imposing growth conditions on f and using a generalization of the multiple fixed point theorem by Leggett-Williams, we show the existence of at least two positive solutions.     

具有转向点的二阶非线性方程Robin问题的奇摄动(英)

本文应用微分不等式的方法，研究了具有转向点的二阶非线性方程Robin问题的奇摄动，根据fy在转向点附近的性态，边值问题的解将呈现冲击层现象和边界层现象，在适当的假设条件下，我们证明了该问题的存在性和不同的渐近性质。     

Nonlinear Approximation from Dictionaries: Some Open Problems: Research Problems 2000-3

No abstract. March 31, 2000. Date accepted: March 31, 2000.     

Some Functions of Points in Projective Spaces

Extending earlier results in the plane, we prove that every n-polygon in sufficiently general position in d-dimensional projective space, n d + 2, gives rise to a derived n-polygon, which preserves a few functions; these functions are the cyclial product of (actually affine) ratios of various points, obtained by proper projections on suitable lines.     

Restricted Nonlinear Approximation

We introduce a new form of nonlinear approximation called restricted approximation . It is a generalization of n -term wavelet approximation in which a weight function is used to control the terms in the wavelet expansion of the approximant. This form of approximation occurs in statistical estimation and in the characterization of interpolation spaces for certain pairs of L _p and Besov spaces. We characterize, both in terms of their wavelet coefficients and also in terms of their smoothness, the functions which are approximated with a specified rate by restricted approximation. We also show the relation of this form of approximation with certain types of thresholding of wavelet coefficients. March 31, 1998. Date accepted: January 28, 1999.     

Functional Optimal Estimation Problems and Their Solution by Nonlinear Approximation Schemes

The design of state estimators for nonlinear dynamic systems affected by disturbances is addressed in a functional optimization framework. The estimator contains an innovation function that has to be chosen within a suitably defined class of functions in such a way to minimize a cost functional given by the worst-case ratio of the ℒ _p norms of the estimation error and the disturbances. Since this entails an infinite-dimensional optimization problem that under general hypotheses cannot be solved analytically, an approximate solution is sought by minimizing the cost functional over linear combinations of simple “basis functions,” represented by computational units with adjustable parameters. The selection of the parameters is made by solving a constrained nonlinear programming problem, where the constraints are given by pointwise conditions that ensure the well-definiteness of the functional and the existence of a solution. Penalty terms are introduced in the cost function to account for constraints imposed on points that result from sampling the sets to which the trajectories of the state and of the estimation error belong. To ensure an efficient covering of the sets, low-discrepancy sampling techniques are exploited that generate samples deterministically spread in a uniform way, without leaving regions of the space undersampled. Work supported by a PRIN grant from the Italian Ministry of University and Research (Project “New Techniques for the Identification and Adaptive Control of Industrial Systems”) and by the EU and the Regione Liguria trough the Regional Programs of Innovative Action of the European Regional Development Fund.     

Product Approximation for Nonlinear Klein-Gordon Equations

^* Current address: Oxford University Computing Laboratory, Oxford, England OX1 3QD. We present convergence results for the Galerkin method withproduct approximation applied to a family of nonlinear Klein-Gordonequations. In the first part of the paper, we obtain error estimatesunder the assumption that a sufficiently smooth solution exists.This is achieved by adapting the method of Douglas and Dupont[6] to the present case. The second part of the paper dealswith the approximation of ‘weak’ solutions and theanalysis relies on a priori estimates satisfied by the approximatesolution.     

用变阶唯一可解函数逼近的两个极限定理

本文用变阶唯一可解函数作为逼近函数,研究了单边逼近对于被逼近函数、逼近域和权函数的相依性,以及有偏逼近与单边逼近的联系。