In this short note, we show that the higher order derivatives of the adjugate matrix $\mbox{Adj}(z-A)$, are related to the nilpotent matrices and projections in the Jordan decomposition of the matrix $A$. These relations appear as a factorization of the derivative of the adjugate matrix as a product of factors related to the eigenvalues, nilpotent matrices and projectors. The novel relations are obtained using the Riesz projector and functional calculus. The results presented here can be considered a generalization of the Thompson and McEnteggert theorem that relates the adjugate matrix with the orthogonal projection on the eigenspace of simple eigenvalues for symmetric matrices. They can also be viewed as a complement to some previous results by B. Parisse, M. Vaughan that related derivatives of the adjugate matrix with the invariant subspaces associated with an eigenvalue. Our results can also be interpreted as a general eigenvector-eigenvalue identity. Many previous works have dealt with relations between the projectors on the eigenspaces and derivatives of the adjugate matrix with the characteristic spaces but it seems there is no explicit mention in the literature of the factorization of the higher-order derivatives of the adjugate matrix as a product involving nilpotent and projector matrices that appears in the Jordan decomposition theorem.
翻译:在这篇简短的文章中,我们展示了伴随矩阵 $\mbox{Adj}(z-A)$ 的高阶导数与$A$ 矩阵相关的 Jordan 分解中的幂零矩阵和投影矩阵的关系。这些关系表现为伴随矩阵导数的分解形式,可以看做是与特征值、幂零矩阵和投影矩阵有关的因子的乘积。这些新颖的结果是通过 Riesz 项目和函数演算得到的。这里所提供的结果可以看作是 Thompson 和 McEnteggert 定理的推广,后者将对称矩阵的伴随矩阵与简单特征值的特征空间上的正交投影相关联。这些结果也可以看作是 B. Parisse 和 M. Vaughan 之前的研究成果的补充,后者将伴随矩阵的导数与与特定特征值相关联的不变子空间相联系。我们的结果也可以被解释为一个一般化的特征向量-特征值恒等式。许多前人的工作涉及到特征空间上的投影矩阵和伴随矩阵的导数以及特征子空间的关系,但是文献中似乎没有直接提到伴随矩阵高阶导数的分解形式,即涉及到在 Jordan 分解定理中出现的幂零矩阵和投影矩阵。