On the monotonicity of weighted power means of matrices

Abstract

Let ${\mu }_p(A,B,t)=(t{A}^p+(1-t)B^p{)}^{1/p}$ denote the weighted power mean between positive operators $A$ and $B$. We show that the function $t\to \Vert A-{\mu }_p(A,B,t){\Vert }_2$ is monotonically decreasing whenever $1/2\le p\le 1$. Hence showing that the weighted power means satisfy Audenaert's "in-betweenness" property for positive operators for power satisfying $1/2\le p\le 1$. We also show that when $p>2$ there exist operators for which the weighted power mean does not satisfy this "in-betweenness" property with respect to the Euclidean metric.

Proposition 4 is not true. Therefore, the article needs major revisions