A note on subadditive matrix functions (Q1613193)

The authors offer results about real-valued subadditive (\(f(X+Y)\leq f(X)+f(Y)\)) functions of matrices, mostly of second order (not distinguished in the paper from the functions \(f_1: \mathbb{R}\to \mathbb{R}\) etc. from which they are extended). For instance, if \(f\) is measurable and \(\sup_{t>0}[f_1(t)/t]\) is finite, then \(f: LG_2(\mathbb{R})\to \mathbb{R}\) is linear.