Let ${\mu }_1$ be a complex number in the numerical range $W\left(A\right)$ of a normal matrix A. In the case when no eigenvalues of A lie in the interior of $W\left(A\right)$, we identify the smallest convex region containing all possible complex numbers ${\mu }_2$ for which $\left[\begin{array}{cc}{\mu }_1& \ast \\ 0& {\mu }_2\end{array}\right]$ is a 2-by-2 compression of A.

中文翻译：

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Ritz 值在正态矩阵的数值范围内的位置

让 ${\mu }_1$ 是数值范围内的复数 $宽\left(\mathrm{一种}\right)$的正规矩阵A。当A 的特征值不存在于$宽\left(\mathrm{一种}\right)$，我们确定包含所有可能的复数的最小凸区域 ${\mu }_2$ 为此 $\left[\begin{array}{cc}{\mu }_1& ＊\\ 0& {\mu }_2\end{array}\right]$是的2×2压缩甲。