
The Hadamard product \([a_{ij}]\circ\) \([b_{ij}]\)of two \(m\times n\) matrices is the entrywise product \([a_{ij}b_{ij}].\) Let \(A_{1},\dots,A_{k}\) be positive semidefinite \(n\times n\) matrices and let \(R\) be the range of \(A_{1} \circ\dots\circ A_{k}\). The authors prove that \(R\) is spanned by the set \(\{A_{1}x_{1}\circ\dots\circ A_{k}x_{k}~| ~x_{1},\dots,x_{k}\in\mathbb{C}^{n} \}\), and even by the smaller set \(\{A_{1}x\circ\dots\circ A_{k} x~| ~x\in\mathbb{C}^{n}\}\). As a corollary, for any complex \(n\times n\) matrices \(B_{1},\dots,B_{k}\), the range of \(B_{1}B_{1}^{\ast}\circ\dots\circ B_{k}B_{k}^{\ast}\) is spanned by \(\{B_{1}x_{1}\circ\dots\circ B_{k}x_{k}~| ~x_{1},\dots,x_{k}\in\mathbb{C}^{n}\}\) (but not by the smaller set with the \(x_{i}\) all equal). This generalizes a result of \textit{X. Sun, X. Du} and \textit{D. Liu} [Linear Algebra Appl. 416, No. 2--3, 868--871 (2006; Zbl 1106.15020)].
Numerical Analysis, Vector spaces, linear dependence, rank, lineability, Eigenvalues, singular values, and eigenvectors, Hadamard product, Algebra and Number Theory, range, Discrete Mathematics and Combinatorics, Hermitian, skew-Hermitian, and related matrices, Span, Geometry and Topology, Range
Numerical Analysis, Vector spaces, linear dependence, rank, lineability, Eigenvalues, singular values, and eigenvectors, Hadamard product, Algebra and Number Theory, range, Discrete Mathematics and Combinatorics, Hermitian, skew-Hermitian, and related matrices, Span, Geometry and Topology, Range
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