
The authors prove that if \(A\) and \(B\) are two \(n\)-by-\(n\) nonzero positive semidefinite matrices and \(\|\cdot\|\) is a unitarily invariant norm on matrices satisfying \(\|\text{diag}(1,0,\dots, 0)\|\geq 1\), then the inequalities \[ {\| AB\|\over\| A\|\,\| B\|}\leq {\| A+ B\|\over\| A\|+\| B\|}\quad\text{and}\quad {\| A\circ B\|\over \| A\|\,\| B\|}\leq {\| A+ B\|\over\| A\|+\| B\|} \] hold, where \(AB\) and \(A\circ B\) denote the usual product and the Hadamard (or Schur) product of \(A\) and \(B\). They also elaborate on this theme and derive other inequalities concerning the parallel sum of \(A\) and \(B\) and the product and Hadamard product of \(A^\alpha\) and \(B^\alpha\) for \(\alpha\geq 1\).
Parallel sum, Numerical Analysis, Hadamard product, Algebra and Number Theory, Matrix Young inequality, Submultiplicativity, Unitarily invariant norm, Positive semidefinite matrix, Miscellaneous inequalities involving matrices, Subadditivity, Norms of matrices, numerical range, applications of functional analysis to matrix theory, Discrete Mathematics and Combinatorics, Majorization, Geometry and Topology
Parallel sum, Numerical Analysis, Hadamard product, Algebra and Number Theory, Matrix Young inequality, Submultiplicativity, Unitarily invariant norm, Positive semidefinite matrix, Miscellaneous inequalities involving matrices, Subadditivity, Norms of matrices, numerical range, applications of functional analysis to matrix theory, Discrete Mathematics and Combinatorics, Majorization, Geometry and Topology
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