On the Set of Possible Minimizers of a Sum of Convex Functions

Abstract

Consider a sum of convex functions, where the only information known about each individual summand is the location of a minimizer. In this letter, we give an exact characterization of the set of possible minimizers of the sum. Our results cover several types of assumptions on the summands, such as smoothness or strong convexity. Our main tool is the use of necessary and sufficient conditions for interpolating the considered function classes, which leads to shorter and more direct proofs in comparison with previous work. We also address the setting where each summand minimizer is assumed to lie in a unit ball, and prove a tight bound on the norm of any minimizer of the sum.