Canonical angles and limits of sequences of EP and co-EP matrices

摘要

Let A be a square complex matrix. Let P be one of the following properties: (a) A is an EP matrix, (b) the column space of A is complementary to the column space of A∗, and (c) the orthogonal complement of the column space of A is the column space of A∗. We study the canonical angles between the column space of A and the column space of A∗ when A satisfies property P. Also, we research the following problem: Let {Am}m=1∞ be a sequence of matrices satisfying property P that converges to some matrix A. When does A satisfy property P?