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arXiv 1012.2254math.FA
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关于凹函数和凸函数的范数次可加性和超可加性不等式

On norm sub-additivity and super-additivity inequalities for concave and convex functions

Koenraad M. R. Audenaert, Jaspal Singh Aujla

摘要:

一段时间以来,多位作者将凹函数和凸函数的次可加不等式和超可加不等式推广到矩阵的情况。这些导致了一些有趣的矩阵不等式,在某些情况下与相应的实数不等式一致,而在其他情况下与之不同。我们调查这些矩阵不等式,并做进一步的调查。我们引入了新的概念,占主导地位的优势之间的频谱的两个埃尔米特矩阵$B$和$C$,占主导地位的第三个埃尔米特矩阵$A$。基于埃尔米特矩阵的$k$最大特征值之和的梯度的显式公式,我们证明了在一定条件下,控制约化为$B$和$C$的对角元素之间在一定基上的线性控制关系.我们使用这个概念作为一个工具,给新的,初步的证明,次可加性不等式的非负凹函数首次证明的Bourin和内山和相应的超可加性不等式的非负凸函数首次证明的Kosem。最后,我们给出了算子凸函数的Ando不等式更一般成立的反例,例如对于普通凸非负函数。

英文摘要:

Sub-additive and super-additive inequalities for concave and convex functions have been generalized to the case of matrices by several authors over a period of time. These lead to some interesting inequalities for matrices, which in some cases coincide with, and in other cases are at variance with the corresponding inequalities for real numbers. We survey some of these matrix inequalities and do further investigations into these. We introduce the novel notion of dominated majorization between the spectra of two Hermitian matrices $B$ and $C$, dominated by a third Hermitian matrix $A$. Based on an explicit formula for the gradient of the sum of the $k$ largest eigenvalues of a Hermitian matrix, we show that under certain conditions dominated majorization reduces to a linear majorization-like relation between the diagonal elements of $B$ and $C$ in a certain basis. We use this notion as a tool to give new, elementary proofs for the sub-additivity inequality for non-negative concave functions first proved by Bourin and Uchiyama and the corresponding super-additivity inequality for non-negative convex functions first proven by Kosem. Finally, we present counterexamples to some conjectures that Ando's inequality for operator convex functions could more generally hold, e.g.\ for ordinary convex, non-negative functions.

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