Certain Linear Combinations of Exponential Functions are Positive under Semidefinite Linear Constraints

Abstract

In this article, I introduce a group-theoretical method to prove positivity of certain linear combinations (with coefficients generally lying in $\mathbb{C}$) of exponential functions under a set of semidefinite linear constraints. The basic group-theoretic fact we rely on is the positivity of the fusion coefficients for multiplication of group characters.