无界2×2分块算子矩阵的本质谱与Weyl谱

研究无界2×2分块算子矩阵是Fredholm算子、Weyl算子的充要条件;给出了次对角元占优2×2分块算子矩阵的本质谱、Weyl谱与其子块算子本质谱、Weyl谱的关系;研究了主对角元占优2×2分块算子矩阵的本质谱、Weyl谱与其子块算子本质谱、Weyl谱的关系.     

无穷维Hamilton算子的二次数值域

研究了一类无界无穷维Hamilton算子的二次数值域的性质,进而,应用二次数值域来刻画了无穷维Hamilton算子谱的分布范围,并给出了二次数值域的闭包包含谱集的结论.     

3×3上三角算子矩阵值域的闭性研究

令H_1,H_2,H_3是可分的复Hilbert空间,记M=(AEF0BD00C)为H_1⊕H_2⊕H_3上的3×3上三角算子矩阵.设A∈B(H_1),B∈B(H_2),C∈B(H_3)是给定的算子,利用对角元算子A,B,C的值域和零空间性质描述了算子矩阵M值域R(M)的闭性.     

有界上三角算子矩阵的亏谱

讨论了希尔伯特空间上有界上三角算子矩阵的亏谱扰动性质,当对角元算子给定时,得到上三角算子矩阵的亏谱恰等于对角元算子的亏谱之并集的充要条件,特别地,给出有界上三角Hamilton型算子矩阵相应问题成立的条件,并辅以实例佐证.     

Hamilton算子矩阵的半群生成性质

本文研究Hamilton算子矩阵生成压缩半群的问题,采用对角元算子的耗散性刻画整个算子的耗散性,借助空间分解和二次补描述右半实轴包含于整体算子的预解集,进而给出若干半群生成的充分必要条件.     

具有单值扩张性的上三角算子矩阵半Fredholm性及其应用

本文研究了具有单值扩张性的上三角算子矩阵半Fredholm性,利用单值扩张性与分块算子升标、降标、零维、亏维之间的联系,得到了具有单值扩张性的上三角算子矩阵半Fredholm性刻画,给出了用对角算子刻画上三角算子矩阵半Fredholm性的条件,并研究了算子矩阵半Fredholm性的扰动问题;此外,利用所得结果研究了上三角算子矩阵的谱、本质谱和Browder谱,同时进一步考虑了Browder定理,a-Browder定理,Weyl定理,a-Weyl定理,从局部谱的角度揭示了定理之间的联系,得到了定理成立的新条件并举例验证.     

辛对称Hamilton算子值域的闭性

利用扰动理论和算子矩阵的因式分解,研究了辛对称Hamilton算子值域的闭性.针对对角占优、上行占优等情形,在一定条件下给出了值域闭性的若干描述,并得到了一般情形的结果.     

2×2分块对角算子矩阵拟谱的精细刻画

设A,B为可分Hilbert空间X中的稠定闭线性算子,■表示2×2分块算子矩阵.文中精细刻画算子矩阵M₀在对角扰动情形下的拟点谱、拟剩余谱与拟连续谱,所得结论与点谱、剩余谱和连续谱的结果进行了比较,并用例子进行了辅证.最后,采用空间分解技巧,用主对角元的信息刻画M₀在上三角扰动情形下的拟点谱分布.     

2×2上三角无界算子矩阵的谱

本文研究了Hilbert空间中的对角定义的2×2上三角闭线性算子矩阵的谱、近似点谱、亏谱和本质谱的性质,进而得到了算子矩阵的谱、近似点谱和亏谱分别等于对角算子的谱、近似点谱和亏谱的并集的充要条件;还得到了算子矩阵的本质谱等于对角算子的本质谱的并集的充分条件.作为应用,本文还得到了对角定义的上三角无穷维Hamilton算子的谱性质.     

非archimedean Banach 空间上算子的值域包含定理

本文给出了几个关于一般赋值域上Banach 空间上的算子的值域包含定理. 这些定理说明: 算子的值域包含、算子的强弱以及算子的分解之间有着重要的联系. 我们发现, 这些结果强烈地依赖于空间的连续延拓性质. 在经典情况下, Hahn-Banach 定理保证了连续延拓性质自然满足; 然而, 在非 archimedean 范畴下, 这种性质可能并不满足. 我们还给出一些反例说明, 这些结果在某种意义下已经不能再改进了.     

Spectral inclusion for unbounded block operator matrices

In this paper we establish a new analytic enclosure for the spectrum of unbounded linear operators A admitting a block operator matrix representation. For diagonally dominant and off-diagonally dominant block operator matrices, we show that the recently introduced quadratic numerical range W²(A) contains the eigenvalues of A and that the approximate point spectrum of A is contained in the closure of W²(A). This provides a new method to enclose the spectrum of unbounded block operator matrices by means of the non-convex set W²(A). Several examples illustrate that this spectral inclusion may be considerably tighter than the one by the usual numerical range or by perturbation theorems, both in the non-self-adjoint case and in the self-adjoint case. Applications to Dirac operators and to two-channel Hamiltonians are given.     

一类无界算子矩阵的本质谱

本文研究了次对角占优的无界算子矩阵M=(ABCD)的左本质谱和本质谱.利用分析方法和分块算子的性质,得到了整个算子矩阵的本质谱(左本质谱)与其内部元素的本质谱(左本质谱)之间的关系.     

A new concept for block operator matrices:the quadratic numerical range

In this paper a new concept for 2×2-block operator matrices – the quadratic numerical range – is studied. The main results are a spectral inclusion theorem, an estimate of the resolvent in terms of the quadratic numerical range, factorization theorems for the Schur complements, and a theorem about angular operator representations of spectral invariant subspaces which implies e.g. the existence of solutions of the corresponding Riccati equations and a block diagonalization. All results are new in the operator as well as in the matrix case.     

A variational principle for block operator matrices and its application to the angular part of the Dirac operator in curved spacetime

The operator associated to the angular part of the Dirac equation in the Kerr-Newman background metric is a block operator matrix with bounded diagonal and unbounded off-diagonal entries. The aim of this paper is to establish a variational principle for block operator matrices of this type and to derive thereof upper and lower bounds for the angular operator mentioned above. In the last section, these analytic bounds are compared with numerical values from the literature.     

Approximation of the Quadratic Numerical Range of Block Operator Matrices

In this paper we establish an approximation of the quadratic numerical range of bounded and unbounded block operator matrices by variational methods. Applications to Hain?CLüst operators are given.     

Symmetry of the Quadratic Numerical Range and Spectral Inclusion Properties of Hamiltonian Operator Matrices

This paper studies Hamiltonian operator matrices with unbounded entries. Their quadratic numerical range is shown to be symmetric with respect to the imaginary axis under certain assumptions. Spectral inclusion properties are found.

     

Noncommuting Domination in Krein Spaces Via Commutators of Block Operator Matrices

The commutators of 2 × 2 block operator matrices with (unbounded) operator entries are investigated. The matrix representation of a symmetric operator in a Krein space is exploited. As a consequence, the domination result due to Cichoń, Stochel and Szafraniec is extended to the case of Krein spaces.     

On Eigenvalues of Split Quaternion Matrices

The main purpose of this paper is to set a method of finding eigenvalues of split quaternion matrices. In particular, we will give an extension of Gershgorin theorem, which is one of the fundamental theorems of complex matrix theory, for split quaternion matrices.     

The block numerical range of matrix polynomials

Block numerical ranges of matrix polynomials, especially the quadratic numerical range, are considered. The main results concern spectral inclusion, boundedness of the block numerical range, an estimate of the resolvent in terms of the quadratic numerical range, geometrical properties of the quadratic numerical range, and inclusion between block numerical ranges of the matrix polynomials for refined block decompositions. As an application, we connect the quadratic numerical range with the localization of the spectrum of matrix polynomials.