摘要
设A=(A1,A2,…,An),B=(B1,B2,…,Bn),其中Ai,Bi∈B(H),i=1,2,…,n,定义初等算子RA,B:B(H)→B(H),MA1,B1:B(H)→B(H),分别为RA,B(X)=∑ni=1AiXBi,MA1,B1(X)=A1XB1,X∈B(H).记d(RA,B)为RA,B作用在H上所有的单位一秩算子的范数的上确界.利用d(RA,B)=∑ni=1‖Ai‖‖Bi‖成立的充要条件及正规代数数值域的定义,研究了d(RA,B)的一些性质,给出了n=2时d(RA,B)=‖A1‖‖B1‖+‖A2‖‖B2‖成立的新的充要条件并且估计了d(MA1,B1+MI,B2)的下界.
For two n-tuples A=(A1 ,A2,…,An),B=(B1 ,B2,…,Bn),Ai,Bi ∈ β(H), i= 1,2,…,n, theelementary operators RA,B;β(H)→β(H) and MA1,B1:β(H)→β(H) are defined respectively by RA,B(X)=∑i=1^nAiXBi,MA1,B1(X)=A1SB1,AX∈β(H) ,d(RA,B)is denoted by the supremum of the norm of RA,B over all unit rank one operators on H.According to the sufficient and necessary conditions for d(RA,B) =∑i=1^n||Ai|| ||Bi||and the definition of the normalized algebraic numerical range, some properties of d (RA,B) are studied. And a new sufficient and necessary condition for d(RA.B)=||A1|| ||B1||+||A2|| ||B2|| for n=2 and the lower bound of d(MA1,B1 + M1,B2 ) are given.
出处
《纺织高校基础科学学报》
CAS
2007年第4期396-399,共4页
Basic Sciences Journal of Textile Universities
基金
国家自然科学基金资助项目(10571114)
陕西省自然科学基础研究计划资助项目(2005A1)
关键词
初等算子
范数
数值域
elementary operator
norm
numerical range