Author

Kai Fang

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Preprint Oct 2026

Extreme points of the unit balls and isometries of noncommutative quasi-Banach Marcinkiewicz spaces

We characterize extreme points of the (positive) unit balls of Marcinkiewicz spaces with respect to their natural quasi-norms. Having these results at hand, we show that every positive surjective isometry on a noncommutative Marcinkiewicz space is of elementary form. In particular, a linear mapping on a noncommutative...

Kai Fang, Yi-Yun Gao, Jing-Hao Huang et al. · 0 citations

Preprint Aug 2026

Jensen's trace inequality with equality condition and noncommutative Lamperti's theorem

Let $\mathcal M$ be a semifinite von Neumann algebra equipped with a semifinite faithful normal trace $\tau$. We establish Jensen's trace inequality in full generality and characterize its equality case, which answers two questions raised in [Kosaki2013] and [HaradaKosaki2008]. As an application, we derive noncommutati...

Kai Fang, Xin He, Jing-Hao Huang · 0 citations