Newton Polytopes and Relative Entropy Optimization

TL;DR

This paper introduces new structural insights into SAGE certificates for certifying signomial nonnegativity, enabling efficient convex relaxation methods for a broad class of nonconvex optimization problems, including polynomial cases.

Contribution

It characterizes the extreme rays of SAGE cones, links Newton polytope structure to nonnegativity certification, and broadens the class of problems solvable via convex relaxation.

Findings

SAGE certificates can be characterized by extreme rays and sparsity.

Signomial nonnegativity is equivalent to SAGE decomposition under certain conditions.

Polynomial nonnegativity certification can be achieved efficiently, independent of degree.

Abstract

Certifying function nonnegativity is a ubiquitous problem in computational mathematics, with especially notable applications in optimization. We study the question of certifying nonnegativity of signomials based on the recently proposed approach of Sums-of-AM/GM-Exponentials (SAGE) decomposition due to the second author and Shah. The existence of a SAGE decomposition is a sufficient condition for nonnegativity of a signomial, and it can be verified by solving a tractable convex relative entropy program. We present new structural properties of SAGE certificates such as a characterization of the extreme rays of the cones associated to these decompositions as well as an appealing form of sparsity preservation. These lead to a number of important consequences such as conditions under which signomial nonnegativity is equivalent to the existence of a SAGE decomposition; our results represent the broadest-known class of nonconvex signomial optimization problems that can be solved efficiently via convex relaxation. The analysis in this paper proceeds by leveraging the interaction between the convex duality underlying SAGE certificates and the face structure of Newton polytopes. While our primary focus is on signomials, we also discuss how our results provide efficient methods for certifying polynomial nonnegativity, with complexity independent of the degree of a polynomial.