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Sherman-Morrison formula in the complex space

To get the inverse of $ ( \lambda^{2} \mathbf{I} +
\mathbf{S^{*}}_{m,n,l} \mathbf{S^{T}}_{m,n,l}) $ , one can implement Sherman-Morrison formula to transform the inverse matrix as (13). Whereas $ \mathbf{S^{*}}_{m,n,l} $ and $ \mathbf{S^{T}}_{m,n,l} $ are complex vectors. Here, we drop the subscript of vectors for a concise proof:

$\displaystyle \begin{aligned}
& (\lambda^{2} \mathbf{I} + \mathbf{S^{*}S^{T}})...
... } { \lambda^{2} + \mathbf{ S^{T}S^{*} }} \\
& = \mathbf{ I },
\end{aligned}$

where $ \mathbf{I}$ denotes the identity matrix, $ \mathbf{S}$ is the complex column vector, $ \mathbf{S^{T}}$ is the transpose of $ \mathbf{S}$ , $ \mathbf{S^{*}}$ is the conjugation of $ \mathbf{S}$ . Therefore, $ \mathbf{S^{*}S^{T}} $ is a complex matrix, and $ \mathbf{S^{T}S^{*}} $ is constant. Therefore, we prove that Sherman-Morrison formula can be applied in the complex space.




2022-04-21