最小二P乘法

1问题的提出最小二乘逼近和最佳一致逼近是数值逼近和曲线拟合中常用的方法,是一对既相同又不同的逼近.二者的相同处在于,都是以误差作为度量的依据;都是以误差的极小化作为逼近的目标.二者的不同点在于,最小二乘逼近是以误差平方和的极小化作为逼近的准则,而最佳一致逼近则是以最大绝对值误差的极小化作为逼近准则的.两种逼近之间异同,     

计算机辅助几何设计中极小曲面造型的研究进展

极小曲面在工程领域有着广泛应用,因此将其引入计算机辅助几何设计领域具有重要意义.详细概述了近年来计算机辅助几何设计领域中极小曲面造型的研究工作,按照造型方法的不同,可将现有工作分为精确造型方法和逼近造型方法两类.精确造型方法主要包括两个部分:某些特殊极小曲面的控制网格表示与构造;等温参数多项式极小曲面的挖掘与性质.逼近造型方法主要包括3个部分t基于数值计算的逼近方法;基于线性偏微分方程的逼近方法;基于能量函数最优化的逼近方法.最后对这些方法进行了分析比较,并讨论了极小曲面造型中有待进一步解决的问题.     

平衡问题变分包含问题及不动点问题的二次极小化

借助预解式技巧,寻求二次极小化问题minx∈Ω‖x‖2的解,其中Ω是Hilbert空间中某一广义平衡问题的解集,与一无穷族非扩张映像的公共不动点的集合,以及某一变分包含的解集的交集．在适当的条件下,逼近上述极小化问题的解的一新的强收敛定理被证明．     

与渐近非扩张半群不动点问题相关的分裂等式混合均衡问题及其应用

研究了与渐近非扩张半群不动点问题相关的分裂等式混合均衡问题.在等式约束下,为同时逼近两个空间中混合均衡问题和渐近非扩张半群不动点问题的公共解,借助收缩投影方法引出了一种迭代程序.在适当条件下,该迭代算法的强收敛性被证明.文末还把所得结果应用于分裂等式混合变分不等式问题和分裂等式凸极小化问题.     

关于BL_p(φ)(Bα)范数下逼近的极小误差问题

本文讨论了BL_p(φ)(Ba)范数意义下的解析函数逼近的极小误差问题。得到了相应于L_p-范数下解析函数逼近的极小误差的结果。从而推广了文[6]和[7]的结果。     

求解约束极小极大问题的一种K─S函数的近似迭代法

借助于极大熵方法和逼近法，给出了一种求解约束极小极大问题的K－S函数近似迭代法，同时讨论算法的有关收敛性．     

约束极小极大问题的一种既约梯度近似法

利用极大熵方法及有关逼近结果，使之与既约梯度法结合，提出了一种求解极小极大非线性规划问题的近似法，并证明了算法的有关收敛性结果。     

极大熵方法与二次规划子问题的显式解

本文对混合约束极大极小问题的目标函数与约束分别用熵函数来逼近,讨论了逼近问题的二次规划子问题的搜索方向的显式形式,并给出了极大极小问题和多目标规划的二次规划予问题的显式解。将所得结果用于相应的算法中,可提高算法的有效性。     

纯正半群上的同余扩张(一)

刻划半群上的同余及其扩张是半群的代数理论中的一个非常重要的课题．本文讨论了带上的同余的正规性和不变性以及在其Ｈａｌｌ半群上的扩张，从同余扩张的角度刻划了带上的同余的性质，给出了扩张的极大、极小同余的描述．     

完全分配格上的弱辅助序与广义序同态

为研究格上的拓扑学,王国俊在[1]中定义了完全分配格上广义序同态概念,并得到一系列重要的结果。刘应明在这方面也进行了深入的研究。本文利用完全分配格上一个逼近的弱辅助序给出广义序同态的一个内在的特征性质与极小集的刻划,并得到保极小集映射的两个等价条件。在此基础上,我们建立了广义序同态的新的扩张定理,然后讨论了以广义序同态为态射的完全分配格范畴的对偶定理,并在乘积范畴上引进一个重要而有趣的函子。     

Extensions of block-projections methods with relaxation parameters to inconsistent and rank-deficient least-squares problems

There exist many classes of block-projections algorithms for approximating solutions of linear least-squares problems. Generally, these methods generate sequences convergent to the minimal norm least-squares solution only for consistent problems. In the inconsistent case, which usually appears in practice because of some approximations or measurements, these sequences do no longer converge to a least-squares solution or they converge to the minimal norm solution of a “perturbed” problem. In the present paper, we overcome this difficulty by constructing extensions for almost all the above classes of block-projections methods. We prove that the sequences generated with these extensions always converge to a least-squares solution and, with a suitable initial approximation, to the minimal norm solution of the problem. Numerical experiments, described in the last section of the paper, confirm the theoretical results obtained.     

Residual type a posteriori error estimates for elliptic obstacle problems

Summary. A posteriori error estimators of residual type are derived for piecewise linear finite element approximations to elliptic obstacle problems. An instrumental ingredient is a new interpolation operator which requires minimal regularity, exhibits optimal approximation properties and preserves positivity. Both upper and lower bounds are proved and their optimality is explored with several examples. Sharp a priori bounds for the a posteriori estimators are given, and extensions of the results to double obstacle problems are briefly discussed. Received June 19, 1998 / Published online December 6, 1999     

Arithmetic properties of three-dimensional algebraic tori

We compute the Shafarevich-Tate group, the kernel of the weak approximation and the Manin groups of three-dimensional algebraic tori defined over an algebraic number field. A minimal example of a torus with fractional Tamagawa number is constructed. A criterion for the validity of the Hasse norm principle for extensions of degree four of an algebraic number field is given.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 116, pp. 102–107, 1982.The author expresses his gratitude to V. E. Voskresenskii and A. A. Klyachko for valuable discussions.     

Height Preserving Minimal Interval Extensions

We consider minimal interval extensions of a partial order which preserve the height of each vertex. We show that minimal interval extensions having this property bijectively correspond to the maximal chains of a sublattice of the lattice of maximal antichains of the given order. We show that they also correspond to the set of minimal interval extensions of a certain extension of this order.     

Extensions of commutative rings

In studying the minimal prime spectra of commutative rings with identity we have been able to identify several interesting types of extensions of rings. In particular, we determine what kind of ring extensions will result in a homeomorphisms of the hull-kernel and inverse topologies on the minimal prime spectra. We relate these types of extensions to other known types of extensions.     

On the spectral theory of the Bessel operator on a finite interval and the half-line

We study the minimal and maximal operators generated by the Bessel differential expression on a finite interval and the half-line. We describe the domains of the Friedrichs and Krein extensions of the minimal operator and all nonnegative self-adjoint extensions of the minimal operator.     

On Minimal Extensions of Rings

Given two rings R ? S, S is said to be a minimal ring extension of R, if R is a maximal subring of S. In this article, we study minimal extensions of an arbitrary ring R, with particular focus on those possessing nonzero ideals that intersect R trivially. We will also classify the minimal ring extensions of prime rings, generalizing results of Dobbs, Dobbs &; Shapiro, and Ferrand &; Olivier, on commutative minimal extensions.     

Approximation of eigenvalues below the essential spectra of singular second-order symmetric linear difference equations

This paper is concerned with approximation of eigenvalues below the essential spectra of singular second-order symmetric linear difference equations with at least one endpoint in the limit point case. A sufficient condition is firstly given for that the k-th eigenvalue of a self-adjoint subspace (relation) below its essential spectrum is exactly the limit of the k-th eigenvalues of a sequence of self-adjoint subspaces. Then, by applying it to singular second-order symmetric linear difference equations, the approximation of eigenvalues below the essential spectra is obtained, i.e., for any given self-adjoint subspace extension of the corresponding minimal subspace, its k-th eigenvalue below its essential spectrum is exactly the limit of the k-th eigenvalues of a sequence of constructed induced regular self-adjoint subspace extensions.     

N-free orders and minimal interval extensions

We investigate problems related to the set of minimal interval extensions of N-free orders. This leads us to a correspondence between this set for an arbitrary order and a certain set of its maximal N-free reductions. We also get a 1-1-correspondence between the set of linear extensions of an arbitrary order and the set of minimal interval extensions of the linegraph of that order. This has an algorithmic consequence, namely the problem of counting minimal interval extensions of an N-free order is #P-complete. Finally a characterization of all N-free orders with isomorphic root graph is given in terms of their lattice of maximal antichains; the lattices are isomorphic iff the root graphs agree.This work was supported by the PROCOPE Program. The first author is supported by the DFG.     

Best Approximation in Numerical Radius

Let X be a reflexive Banach space. In this article, we give a necessary and sufficient condition for an operator T ∈ 𝒦(X) to have the best approximation in numerical radius from the convex subset 𝒰 ? 𝒦(X), where 𝒦(X) denotes the set of all linear, compact operators from X into X. We also present an application to minimal extensions with respect to the numerical radius. In particular, some results on best approximation in norm are generalized to the case of the numerical radius.