We give several criteria that are equivalent to the basic singular value majorization inequality (1.1) that is common to both the usual and Hadamard products. We then use these criteria to give a uniied proof of the basic majorization inequality for both products. Finally, we introduce natural generalizations of the usual and Hadamard products and show that although these generalizations do not...

Using a quasilinear representation for unitarily invariant norms, we prove a basic inequality: Let A = L X X M be positive semideenite, where X 2 M m;n. Then k jX j p k 2 kL p k kM p k for all p > 0 and all unitarily invariant norms k k. We show how several inequalities of Cauchy-Schwarz type follow from this bound and obtain a partial analog of our results for l p norms.

Applications in constrained optimization (and other areas) produce symmetric matrices with a natural block 2 2 structure. An optimality condition leads to the problem of perturbing the (1,1) block of the matrix to achieve a speci®c inertia. We derive a perturbation of minimal norm, for any unitarily invariant norm, that increases the number of nonnegative eigenvalues by a given amount, and we s...

Let Cm×n, Cm×n r , C m ≥ , C m > , and In denote the set of m × n complex matrices, subset of Cm×n consisting of matrices with rank r, set of the Hermitian nonnegative definite matrices of order m, subset of C ≥ consisting of positive-definite matrices and n × n unit matrix, respectively. Without specification, we always assume that m > n >max{r, s} and the given weight matrices M ∈ C > ,N ∈ C ...

Assuming only that the spectra of A and B are disjoint as opposed to the more restrictive assumption previously used, we obtain a bound in all unitarily invariant norms on the solution to the structured Sylvester equation AX − XB = A1/2EB1/2. This bound is the first of its kind in all unitarily invariant norms under only the disjointedness assumption. An application of the bound to the relative...