Quadratic Inequalities for Hilbert Space Operators

Properties of sets of solutions to inequalities of the form

Sup and Max Properties for the Numerical Radius of Operators in Banach Spaces

The article deals with the following problem: given a bounded linear operator A in a Banach space X, how can multiplication of A by an operator of norm one (contraction) affect the numerical radius of A? The approach used in this work is close to that employed by Vieira and Kubrusly in 2007 for their study concerning spectral radius. It turns out that this study is closely related to the study of V-operators conducted in 2005 by Khatskevich, Ostrovskii, and Shulman; the results of this article demonstrate that in certain cases the obtained property of an operator implies that it is a V-operator, while in some other cases the converse is true.     

张量对称类上诱导线性算子的数值半径

设V是一个n维线性空间,V_x~m(G)为V上的张量对称类.A为V的线性算子T的矩阵,K(A)为V_x~m(G)上的诱导线性算子K(T)的矩阵.本文从K(A)的数值半径Υ(K(A))和可分数值半径Υ_x(K(A))定义出发,研究了Υ(K(A))、Υ_x(K(A))与范数||A||_p(1≤p≤2)、广义矩阵函数d_x~G(A)的关系,得到了它们之间的两个不等式.     

关于矩阵Kronecker积的谱半径的不等式

本文证明了矩阵的 Kronecker积的谱半径的两个不等式     

On Generalized Numerical Ranges of Operators on an Indefinite Inner Product Space

In this article, numerical ranges associated with operators on an indefinite inner product space are investigated. Boundary generating curves, corners, shapes and computer generations of these sets are studied. In particular, the Murnaghan-Kippenhahn theorem for the classical numerical range is generalized.     

Hilbert空间中算子迹的Bellman不等式

本文利用矩阵论和泛函分析知识,证明了在Hilbert空间中算子迹的Bellman不等式tr(AB)^k≤tr(A^kB^k)当A,B为正迹类算子时,对一切自然数k都成立;当A,B为自伴迹类算子时,对一切偶数k都成立.     

带有对称函数的实四数矩阵的广义数值半径

本文定义了带有对称函数的实四无数矩阵的广义数值半径并得到了它们所满足的不等式。     

关于随机矩阵Kronecker积的谱半径的不等式

研究了随机矩阵的Kronecker积的数学期望的性质,得到了随机矩阵的Kronecker积的谱半径的几个不等式.     

关于实四元数矩阵的数值半径

本文在[1]的基础上研究了实四元数矩阵的数值半径。得到了关于数值半径幂的不等式。C-数值半径的不等式也给出了。因此我们推广了曹重光教授的结果。     

随机矩阵函数Kronecker积的谱半径的不等式

证明了随机矩阵函数Kronecker积的谱半径的几个不等式.     

The numerical range of a nilpotent operator on a Hilbert space

We prove that the numerical range of an arbitrary nilpotent operator on a complex Hilbert space is a circle (open or closed) with center at and radius not exceeding where is the power of nilpotency of

     

On the Origin and Numerical Range of Bounded Operators

Numerical range has an important applications on spectrum distribution of operators. In this paper, we devoted to characterizing operators whose numerical range contains the origin. Some necessary and sufficient conditions are given by operator decomposition technique and constructive methods. Furthermore, the closeness of the numerical range of a given operator is also investigated.     

Rate of Metastability for Bruck'S Iteration of Pseudocontractive Mappings in Hilbert Space

We give a quantitative version of the strong convergence of Bruck's iteration schema for Lipschitzian pseudocontractions in Hilbert space.     

Numerical radius for the asymptotic stability of delay differential equations

In this note, we make use of the numerical radius to investigate the asymptotic stability of linear systems of delay differential equations. We present examples to illustrate our assumption is weaker than the classical ones.     

Numerical Radii for Tensor Products of Operators

For bounded linear operators A and B on Hilbert spaces H and K, respectively, it is known that the numerical radii of A, B and ${A\otimes B}$ are related by the inequalities ${w(A)w(B)\le w(A\otimes B)\le {\rm min}\{\|A\|w(B), w(A)\|B\|\}}$ . In this paper, we show that (1) if ${w(A\otimes B) = w(A)w(B)}$ , then w(A) = ρ(A) or w(B) = ρ(B), where ρ(·) denotes the spectral radius of an operator, and (2) if A is hyponormal, then ${w(A\otimes B) = w(A)w(B) = \|A\|w(B)}$ . Here (2) confirms a conjecture of Shiu’s and is proven via dilating the hyponormal A to a normal operator N with the spectrum of N contained in that of A. The latter is obtained from the Sz.-Nagy–Foia? dilation theory.     

Analytic Characterization for Hilbert-Schmidt Operators on Fock Space

In this paper we first introduce and investigate some special classes of nonlinear maps and get several useful results. Then, by using these results, we obtain analytic criteria for checking whether or not an operator defined only on the exponential vectors of a symmetric Fock space becomes a Hilbert-Schmidt operator on the whole space. Additionally, as an application, we also get an analytic criterion for Hilbert-Schmidt operators on a Gaussian probability space through the Wiener-Ito-Segal isomorphism.     

Norm Inequalities for Sums of Positive Operators. II

It is shown that if A and B are positive operators on a separable complex Hilbert space, then for every unitarily invariant norm. When specialized to the usual operator norm ||·|| and the Schatten p-norms ||·||_p, this inequality asserts that and These inequalities improve upon some earlier related inequalities. Other norm inequalities for sums of positive operators are also obtained.