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arXiv 2007.14323math.FA
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关于某些算子和矩阵的Stampfli点

On the Stampfli point of some operators and matrices

Thanin Quartz, Ilya M. Spitkovsky

摘要:

算子$A$的质心(记作St($A$),本文中称为A的{ \em Stampfli点})是由Stampfli在他的Pacific J. Math(1970)论文中作为唯一的$λ\in\mathbb C$引入的,它给出了$A-λI$的范数的最小值。我们得到了几类算子St($A$)的位置的一些结果,包括2 × 2块算子矩阵的标量对角块和3 × 3矩阵的重复特征值.我们还表明,几乎正常的$A$的Stampfli点位于凸包的频谱,这是不是在一般情况下。建立了St($A$)=0的性质与$A$对恒等算子的Roberts正交性之间的关系.

英文摘要:

The center of mass of an operator $A$ (denoted St($A$), and called in this paper as the {\em Stampfli point} of A) was introduced by Stampfli in his Pacific J. Math (1970) paper as the unique $λ\in\mathbb C$ delivering the minimum value of the norm of $A-λI$. We derive some results concerning the location of St($A$) for several classes of operators, including 2-by-2 block operator matrices with scalar diagonal blocks and 3-by-3 matrices with repeated eigenvalues. We also show that for almost normal $A$ its Stampfli point lies in the convex hull of the spectrum, which is not the case in general. Some relations between the property St($A$)=0 and Roberts orthogonality of $A$ to the identity operator are established.

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