English

Matrix Inequalities between $f(A)\sigma f(B)$ and $A\sigma B$

Functional Analysis 2024-04-19 v2

Abstract

Let AA and B B be n×nn\times n positive definite complex matrices, let σ\sigma be a matrix mean, and let f:[0,)[0,)f : [0,\infty)\to [0,\infty) be a differentiable convex function with f(0)=0f(0)=0. We prove that f(0)(AσB)f(m)m(AσB)f(A)σf(B)f(M)M(AσB)f(M)(AσB),f^{\prime}(0)(A \sigma B)\leq \frac{f(m)}{m}(A\sigma B)\leq f(A)\sigma f(B)\leq \frac{f(M)}{M}(A\sigma B)\leq f^{\prime}(M)(A\sigma B), where mm represents the smallest eigenvalues of AA and BB and MM represents the largest eigenvalues of AA and BB. If ff is differentiable and concave, then the reverse inequalities hold. We use our result to improve some known subadditivity inequalities involving unitarily invariant norms under certain mild conditions. In particular, if f(x)/xf(x)/x is increasing, then f(A)+f(B)f(M)MA+Bf(A+B)|||f(A)+f(B)|||\leq\frac{f(M)}{M} |||A+B|||\leq |||f(A+B)||| holds for all AA and BB with MA+BM\leq A+B. Furthermore, we apply our results to explore some related inequalities. As an application, we present a generalization of Minkowski's determinant inequality.equality.

Keywords

Cite

@article{arxiv.2302.08127,
  title  = {Matrix Inequalities between $f(A)\sigma f(B)$ and $A\sigma B$},
  author = {Manisha Devi and Jaspal Singh Aujla and Mohsen Kian and Mohammad Sal Moslehian},
  journal= {arXiv preprint arXiv:2302.08127},
  year   = {2024}
}

Comments

to appear in Aequationes Mathematicae