算子空间的原子性

研究了算子空间的原子性.证明了算子空间V是原子当且仅当V是正合且有限内射; V内的任意一个有限维算子子空间是原子当且仅当V是原子且V内任意有限维算子子空间足V的完全补.因此作为推论,得到了无限维箅子空间V的任意有限维子空间是原子,则V是1-Hilbertian和1-齐次.     

有限秩算子的表示(Ⅰ)

定义了子空间格代数的(弱闭双边)模,对有限维Hilbert空间的强自反子空间格代数的模及原子Boolean格代数的模中的有限秩算子进行了讨论,得到有限秩算子一定可以表示为秩1算子的和.     

有限秩算子的表示（I）

定义了子空间格代数的（弱闭双边）模,对有限维Hilbert空间的强自反子空间格代数的模及原子Boolean格代数的模中的有限秩算子进行了讨论,得到了有限秩算子一定可以表示为秩1算子的和。     

关于线性变换的像空间与核空间的直和

讨论数域P上有限维线性空间V上线性变换A的方幂A~k的像空间ImA~k与核空间KerA~k的直和,并将结论推广到无限维线性空间.证明了:V=ImA~k+KerA~k当且仅当ImA~k=ImA~(k+1),以及ImA~k∩KerA~k=0当且仅当KerA~k=KerA~(k+1).     

欧氏空间子空间正交补的代数方法研究

在n维欧氏空间Rn中,对其任意的非零子空间V1,有子空间V2使V1⊥V2,且Rn=V1V2.本文对这一几何问题利用齐次线性方程组给予了代数方法的又一种证明.     

CN上Fock空间上的有限余维加权复合算子(英文)

本文给出了C^N上Fock空间上有限余维加权复合算子的完全刻画,该刻画与Fock空间上循环向量的刻画密切相关.主要结论表明,Fock空间上一个有界加权复合算子是有限余维的当且仅当其复合符号是1次可逆解析多项式,且当N=1时,其加权符号至多有有限个零点;当N≥2时,其加权符号没有零点.     

p-算子空间上的框架逼近和嵌入

介绍了p-算子空间上的p-完全有界框架概念.证明了可分p-算子空间X上存在p-完全有界框架当且仅当X满足p-完全有界逼近性质当且仅当X能够p-完全可补嵌入有p-完全有界基的p-算子空间.对于满足p-完全有界逼近性质的非可分的p-算子空间,还证明了其任意可分子空间均可以p-完全同构嵌入到有p-完全有界框架的p-算子空间.     

有界对称区域上Dirichlet空间中的紧Toeplitz算子

介绍了有界对称区域Ω上Dirichlet空间中的Toeplitz算子的紧性:如果S是有限个Toeplitz算子乘积的有限和,S是紧算子当且仅当S的Berezin变换S(z)趋于0.     

A^p（φ）上的Toeplitz算子与Berezin变换

讨论了加权Bergman空间A^p(φ）（1＜p＜∞）上的Toeplitz算子的有限乘积的有限和是紧算子当且仅当其Berezin变换在边界趋向于零。     

半Fredholm算子的一些特征

本文给出了希尔伯特空间中的半Fredholm算子的一些特征,证明了三个算子是半Fred-holm算子,当且仅当它的值域在紧扰动和小摄动下均为闭的,并且还证明一个算子是半Fred-holm的当且仅当在小摄动中零空间的维数是有界的.     

赋β-范空间中的最佳逼近问题

This paper deals with the problems of best approximation in β-normed spaces.With the tool of conjugate cone introduced in [1] and via the Hahn-Banach extension theorem of β-subseminorm in [2],the characteristics that an element in a closed subspace is the best approximation are given in Section 2.It is obtained in Section 3 that all convex sets or subspaces of a β-normed space are semi-Chebyshev if and only if the space is itself strictly convex.The fact that every finite dimensional subspace of a strictly convex β-normed space must be Chebyshev is proved at last.     

The unilateral backward shift is w-quasisubscalar

In [Ko 2] we extend Putinar's theorem to every operator on a finite dimensional space by generalizing Putinar's techniques. Using these techniques, we construct a functional model for the unilateral backward shift. We show, in particular, that the unilateral backward shift is w-quasisubscalar. As a corollary we prove that every strict contraction is w-subscalar, i.e., is similar to the restriction to an invariant subspace of a w-scalar operator.Research partially supported by GARC.     

Invariant and Almost-Invariant Subspaces for Pairs of Idempotents

It is known that every bounded operator on an infinite dimensional separable Hilbert space \({\mathcal{H}}\) has an invariant subspace if and only if each pair of idempotents on \({\mathcal{H}}\) has a common invariant subspace. We show that the same equivalence holds for operators and pairs of idempotents that are essentially selfadjoint. We also show that each pair of idempotents on \({\mathcal{H}}\) has a common almost-invariant half-space.     

有界线性算子的摄动定理

本文研究了正则算子的摄动理论.考虑Banach空间X上的正则算子T,假设dim[K(T)∩N(T)]<∞且K(T)闭,则当S∈B(X)可逆,ST=TS,‖S‖充分小时,证明了T—S为上半Fredholm算子.在以上条件下,若K(T)+N(T)或者R(T)+N(T)在X中有有限维的补子空间,这时T—S为Fredholm算子.     

On invariant subspaces for polynomially bounded operators

We discuss the invariant subspace problem of polynomially bounded operators on a Banach space and obtain an invariant subspace theorem for polynomially bounded operators. At the same time, we state two open problems, which are relative propositions of this invariant subspace theorem. By means of the two relative propositions (if they are true), together with the result of this paper and the result of C.Ambrozie and V.Müller (2004) one can obtain an important conclusion that every polynomially bounded operator on a Banach space whose spectrum contains the unit circle has a nontrivial invariant closed subspace. This conclusion can generalize remarkably the famous result that every contraction on a Hilbert space whose spectrum contains the unit circle has a nontrivial invariant closed subspace (1988 and 1997).     

Pontrjagin空间上一般算子代数弱闭和一致闭的等价条件

本文研究Pontrjagin空间上一般算子代数弱闭和一致闭的等价条件,得到定理:设C0(U),C1(U,L,R,D,V),C2a(U),C2b(U,R),C3a(U),C3b(U,R)分别是Ⅱk空间上第0,Ⅰ,Ⅱa,Ⅱb,Ⅲa和Ⅲb类的算子代数,则(1)C0(U),C2a(U)或C3a(U)为一致闭(弱闭)的等价条件是U是Hibert空间G上的C*-代数(W*-代数;(2)C1(U,L,R,D,V)为一致闭(弱闭)的等价条件是U是Hibert空间H上的C*-代数(W*-代数),并且R是闭子空间,V是闭算子,L对称闭的;(3)C2b(U,R)或C3b(U,R)为一致闭(弱闭)的等价条件是U是Hibert空间H上的C*-代数(W*-代数),并且R是闭子空间．     

Subspace Inclusion Graph of a Vector Space

In this paper, the authors introduce a graph structure, called subspace inclusion graph ?n(𝕍) on a finite dimensional vector space 𝕍 where the vertex set is the collection of nontrivial proper subspaces of a vector space and two vertices are adjacent if one is contained in other. The diameter, girth, clique number, and chromatic number of ?n(𝕍) are studied. It is shown that two subspace inclusion graphs are isomorphic if and only if the base vector spaces are isomorphic. Finally, some properties of subspace inclusion graph are studied when the base field is finite.     

有限维赋范空间至C(Ω)-的等距逼近问题

本文讨论了有限维赋范空间Ｘ至无限维Ｃ（Ω）的等距逼近问题．证明了当Ｘ不是任意ｌ∞ｎ（ｎ∈Ｎ）的子空间且Ω中含无穷多个孤立点时，等距逼近问题不成立；在其它情形该问题都成立．     

THE FUNCTIONAL DIMENSION OF SOME CLASSES OF SPACES

The functional dimension of countable Hilbert spaces has been discussed by some authors. They showed that every countable Hilbert space with finite functional dimension is nuclear. In this paper the authors do further research on the functional dimension, and obtain the following results: (1) They construct a countable Hilbert space, which is nuclear, but its functional dimension is infinite. (2) The functional dimension of a Banach space is finite if and only if this space is finite dimensional. (3) Let B be a Banach space, B* be its dual, and denote the weak * topology of B* by σ(B*,B). Then the functional dimension of (B*,σ(B*,B)) is 1. By the third result, a class of topological linear spaces with finite functional dimension is presented.