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     

Hermitizable,isospectral complex matrices or differential operators

The main purpose of the paper is looking for a larger class of matrices which have real spectrum. The first well-known class having this property is the symmetric one, then is the Hermite one. This paper introduces a new class, called Hermitizable matrices. The closely related isospectral problem, not only for matrices but also for differential operators is also studied. The paper provides a way to describe the discrete spectrum, at least for tridiagonal matrices or one-dimensional differential operators. Especially, an unexpected result in the paper says that each Hermitizable matrix is isospectral to a birth–death type matrix (having positive sub-diagonal elements, in the irreducible case for instance). Besides, new efficient algorithms are proposed for computing the maximal eigenpairs of these class of matrices.     

生灭矩阵重构三弦乐谱

三弦乐谱可由三对角复矩阵生成,人们听到的声音由其谱决定,自然要求此矩阵有实谱.如同量子力学,模型的描述是复算子,可观测量是实的.换言之,所述的三对角复矩阵应是关于某个测度的复内积空间上的自共轭算子.熟知,生灭Q矩阵可配称,自然就是自共轭的.我们将要介绍最新的一个代表性成果:对于相当广泛的自共轭三对角复矩阵,总可以构造出一个生灭Q矩阵,使得两者等谱(简单地说,两者有完全相同的特征值).这个问题浅显易懂,但我们曾在不同时期,从概率论、统计物理和计算数学三个不同的角度研究过,经历了漫长的求索岁月.本文是根据作者在"International Conference on Probability Theory and Its Applications"(湖南文理学院,2018年7月)的报告整理而成.共分三部分:1)生灭过程的新应用;2)从(非对角线元素非负的)实可配称矩阵到复可配称矩阵;3)此课题的来源(计算)及其判别准则的应用(统计物理及量子力学).     

Metric Properties of Projections in Semi-Hilbertian Spaces

Several results on norms of projections on a Hilbert space are extended for the operator seminorm defined by a positive semidefinite operator . The authors were supported in part by UBACYT I030, ANPCYT PICT 03-09521, PIP 2188/00.     

Reflection symmetry and symmetrizability of Hilbert space operators

A general factorization theorem for symmetrizable operators relating their spectra to spectra of selfadjoint operators induced by minimal factorizations is established. Its modified version essentially improves and completes a theorem of Jorgensen, which concerns diagonalizing operators with reflection symmetry.

     

A note on the zero Mach number limit of compressible Euler equations

This note presents a short and elementary justification of the classical zero Mach number limit for isentropic compressible Euler equations with prepared initial data. We also show the existence of smooth compressible flows, with the Mach number sufficiently small, on the (finite) time interval where the incompressible Euler equations have smooth solutions.

     

Spectral analysis of non‐compact symmetrizable operators on Hilbert spaces

This paper revisits and complement in different directions the classical work by W. T. Reid on symmetrizable completely continuous transformations in Hilbert spaces and a more recent paper by one of the authors. More precisely, we deal with spectral properties of % non‐compact operators G on a complex Hilbert space H such that SG is self‐adjoint where S is a (not necessarily injective) nonnegative operator. We study the isolated eigenvalues of G outside its essential spectral interval and provide variational characterization of them as well as stability estimates. We compare them also to spectral objects of SG. Finally, we characterize the Schechter essential spectrum of strongly symmetrizable operators in terms singular Weyl sequences; in particular, we complement J. I. Nieto's paper on the essential spectrum of symmetrizable. Copyright © 2014 John Wiley & Sons, Ltd.     

The spectral properties of certain linear operators and their extensions

Let be a Hilbert space with inner-product , and let be a bounded positive operator on which determines an inner-product, . Denote by the completion of with respect to the norm . In this paper, operators having certain relationships with are studied. In particular, if where , then has an extension , and and have essentially the same spectral and Fredholm properties.

     

Invariant symmetric bilinear forms for reflection groups

In this paper we describe a connection between Vinberg's criterion for the existence of an invariant symmetric bilinear form for a geometric representation of a Coxeter groups and other criteria which are formulated in terms of conjugation invariant sets of reflections generating a given group. Similar methods lead to the result that every non-symmetrizable Kac--Moody Lie algebra contains a non-symmetrizable subalgebra of rank 3. Finally we explain how the results for symmetric bilinear forms can also be obtained for skew-symmetric forms. Received 3 March 2000.