On sum of squares certificates of non-negativity on a strip

Paula Escorcielo, Daniel Perrucci

A well-known result of Murray Marshall states that every $f\in \mathbb{R}[X,Y]$ non-negative on the strip $[0,1]\times \mathbb{R}$ can be written as $f={\sigma }_0+{\sigma }_{1}X(1-X)$ with $…