摘要(英) |
Given an $n$-by-$n$ matrix $A$, the dimension of $ran(I_n-A^ast A)$ is called the defect index of $A$. In this thesis, we make a detailed study of matrices $A$ with the property $rank(I_n-A^ast A)=1$. Let $mathcal{S}_n equiv {A in M_n: rank(I_n-A^ast A)=1: and |lambda|<1 for all lambda in sigma(A)}$ and $mathcal{S}_n^{-1} equiv {A in M_n: rank(I_n-A^ast A)=1 and |lambda|>1 for all lambda in sigma(A)}$. Firstly, we give a complete characterization for matrices of defect index one, namely, $rank(I_n-A^ast A)=1$ if and only if $A$ is unitarily equivalent to either $U oplus B$ or $U oplus C$, where $U$ is a $k times k$ unitary matrix, $0 leq k< n$, $B in mathcal{S}_{n-k}^{-1}$ and $C in mathcal{S}_{n-k}$. Moreover, we also give a complete characterization of $mathcal{S}_n^{-1}$-matrices. We find the polar decompositions of $mathcal{S}_n^{-1}$-matrices. Next, we prove that every $mathcal{S}_n^{-1}$-matrix is irreducible, cyclic, and the boundary of its numerical range is an algebraic curve. Finally, we give the
norm of $mathcal{S}_n^{-1}$-matrices in terms of its eigenvalues. |
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