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The study of the properties of real and complex matrices that are more close to analysis and operator theory. For instance: the properties of positive definite matrices, matrix inequalities, perturbation analysis, matrix functions, inequalities between eigenvectors and singular values, majorization.

5 votes
1 answer
797 views

A matrix norm inequality II

Let $\|\cdot\|$ be the spectral norm, i.e., largest singular value. The condition number of an invertible complex matrix $X$ is defined as $\kappa(X):=\|X\|\|X^{-1}\|$. I am able to prove Propos …
M. Lin's user avatar
  • 1,748
8 votes
2 answers
362 views

Unitary factor in polar decompositions

Let $A, B$ be $n$-square (Hermitian) positive definite matrices. Let $AB=U|AB|$ be the polar decomposition of $AB$. So $U$ is unitary (called the unitary factor of $AB$). What is the optimal constant …
M. Lin's user avatar
  • 1,748
35 votes
3 answers
4k views

A curious determinantal inequality

In my study, I come across the following curious inequality, which I do not know a proof yet (so I am asking it here). Let $A, B$ be $n\times n$ (Hermitian) positive definite matrices. It is very l …
M. Lin's user avatar
  • 1,748
10 votes
1 answer
614 views

A curious determinantal inequality I

Let $A, B$ be Hermitian matrices. Does the following hold? $$\det(A^{2}+B^{2}+|AB+BA|)\leq \det(A^{2}+B^{2}+|AB|+|BA|)$$ As usual, $|X|=(X^*X)^{1/2}$. Clearly, quantities on both sides are no less t …
M. Lin's user avatar
  • 1,748
9 votes
1 answer
800 views

A singular value-eigenvalue inequality

Singular value or eigenvalue problems lie at the center of matrix analysis. One classical result is $$\lambda_{j}(X^{*}X+Y^{*}Y)\geq 2\sigma_j(XY^*)$$ for $j \in \{1, \ldots, n\}$, where $\lambda_j( …
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