Nonnegative Polynomials and Sums of Squares
Abstract
In the smallest cases where there exist nonnegative polynomials that are not sums of squares we present a complete explanation of this distinction. The fundamental reason that the cone of sums of squares is strictly contained in the cone of nonnegative polynomials is that polynomials of degree satisfy certain linear relations, known as the Cayley-Bacharach relations, which are not satisfied by polynomials of full degree 2d. For any nonnegative polynomial that is not a sum of squares we can write down a linear inequality coming from a Cayley-Bacharach relation that certifies this fact. We also characterize strictly positive sums of squares that lie on the boundary of the cone of sums of squares and extreme rays of the cone dual to the cone of sums of squares
Keywords
Cite
@article{arxiv.1010.3465,
title = {Nonnegative Polynomials and Sums of Squares},
author = {Grigoriy Blekherman},
journal= {arXiv preprint arXiv:1010.3465},
year = {2012}
}
Comments
The paper was substantially revised to improve the presentation. The results remain essentially the same, but the presentation is unified and simplified. Accepted in Journal of the AMS