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Majorization and some operator monotone functions. (English) Zbl 1188.47019

Let \(h\) be a non-decreasing function on an interval \(I\) and \(k\) be an increasing function on an interval \(J\). Then \(h\) is said to be majorized by \(k\), denoted by \(h \preceq k\,\,(J)\), if \(J\subseteq I\) and the composite \(h\circ k^{-1}\) is operator monotone on \(k(J)\). The main result of the paper is that \(\frac{t-a}{f(t)-f(a)}\) is a nonnegative operator monotone function if \(f(t)\) is operator monotone on \((0, \infty)\) and \(0 <a<\infty\). The author then utilizes the notion of majorization to conclude that \(\frac{(t-a)(t-b)}{(t^r-a^r )(t^{1-r}-b^{1-r})}\) is operator monotone on \([0,\infty)\) for \(0 \leq a, b < \infty\) and for \(0 \leq r \leq 1\). The special case where \(a = b = 1\) gives rise to a theorem of D.Petz and H.Hasegawa [Lett.Math.Phys.38, No.2, 221–225 (1996; Zbl 0855.58070)].

MSC:

47A63 Linear operator inequalities
15A39 Linear inequalities of matrices

Citations:

Zbl 0855.58070
Full Text: DOI

References:

[1] Bhatia, R., Matrix Analysis (1996), Springer · Zbl 0863.15001
[2] F. Hansen, T. Furuta, Some operator monotone functions, 2008. Arxiv: 0803.2364; F. Hansen, T. Furuta, Some operator monotone functions, 2008. Arxiv: 0803.2364
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[4] Petz, D.; Hasegawa, H., On the Riemannian metric of \(\alpha \)-entropies of density matrices, Lett. Math. Phys., 38, 221-225 (1996) · Zbl 0855.58070
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