自然科学版
陕西师范大学学报(自然科学版)
数学与计算机科学
Weyl型定理的等价性及其判定方法
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张艳华,曹小红*
(陕西师范大学 数学与信息科学学院, 陕西 西安 710062)
张艳华,女, 硕士研究生, 研究方向为算子理论.* 通信作者:曹小红, 女, 教授, 博士. E-mail: xiaohongcao@snnu.edu.cn.
摘要:
研究了Hilbert空间上有界线性算子T的Weyl型定理的判定方法及等价性.根据一致Fredholm指标性质,定义了一种新的谱集σ2(T),通过该谱集和拓扑一致降标集ρτ(T)之间的关系,证明了:算子T满足Browder定理当且仅当ρτ(T)ρb(T)∪σ1(T)∪σ2(T);T满足Weyl定理当且仅当π00(T)ρτ(T)ρb(T)∪σ1(T)∪σ2(T),其中ρb(T)={λ∈C:T-λI为Browder算子},σ1(T)为本质逼近点谱的一种变化,π00(T)为谱集中孤立的有限重的特征值的全体;算子T与T*均满足a-Browder定理当且仅当ρτ(T)ρab(T)∪σ2(T)∪int σSF(T)∪{λ∈C: des (T-λI)<∞},其中ρab(T)={λ∈C:T-λI为上半Fredholm算子且有有限的升标},σSF(T)和des (T)分别表示算子T的半Fredholm谱以及降标.
关键词:
一致Fredholm指标算子; Weyl型定理; 谱
收稿日期:
2010-01-08
中图分类号:
O177.2
文献标识码:
A
文章编号:
1672-4291(2010)05-0018-05
基金项目:
国家自然科学基金资助项目(10726043); 教育部新世纪优秀人才支持计划资助项目(2006).
Doi:
The equivalence and judgement for Weyl type theorems
ZHANG Yan-hua, CAO Xiao-hong*
(College of Mathematics and Information Science, Shaanxi Normal University, Xi′an 710062, Shaanxi, China)
Abstract:
The equivalence and judgement for Weyl type theorems of a bounded linear operator T on a Hilbert space are discussed, a new spectrum σ2 (T) is defined in view of the consistency in Fredholm index. By using the relation between σ2 (T) and ρτ(T), the following conclusions are proved: Browder′s theorem holds for T if and only if ρτ(T)ρb(T)∪σ1(T) ∪σ2(T); T∈B(H) satisfies Weyl′s theorem if and only if π00(T)ρτ(T)ρb(T)∪σ1(T) ∪σ2(T), where ρb(T)={λ∈C: T-λ I is Browder},σ1(T) is a variant of the essential approximate point spectrum, and π00(T) denotes the set of all isolated eigenvalues of finite multiplicity; both T and T* satisfy a-Browder′s theorem if and only if ρτ(T)ρab(T)∪σ2(T)∪int σSF(T)∪ {λ∈C: des (T-λ I)
KeyWords:
consistent Fredholm index operator; Weyl type theorem; spectrum