@article{hansen2002a,
title = {Convex trace functions of several variables},
language = {eng},
author = {Hansen, Frank},
journal = {Linear Algebra and Its Applications},
volume = {341},
number = {1-3},
pages = {309-315},
year = {2002},
issn = {18731856, 00243795},
abstract = {We prove that the function (x1,...,xk)¿Tr(f(x1,...,xk)), defined on k-tuples of symmetric matrices of order (n1,...,nk) in the domain of f, is convex for any convex function f of k variables. The matrix f(x1,...,xk) is defined by the functional calculus for functions of several variables, and it is symmetric and of order n1,...,nk.},
doi = {10.1016/S0024-3795(01)00392-5}
}