Some inequalities for unitarily invariant norms

Abstract

In this note, we use the convexity of the function φ(v) to sharpen the matrix version of the Heinz means, where φ(v) is defined as φ(v) = ||AvXB1-v +A1-vXBv|| on [0,1] for A,B,X ∈ Mn such that A and B are positive semidefinite, and also give a refinement of the inequality [Theorem 6, SIAM J. Matrix Anal. Appl. 20 (1998), 466–470] which is due to Zhan.