Extremal Positive Semidefinite Matrices for Graphs without $K_5$ Minors

Liam Solus, Caroline Uhler, Ruriko Yoshida

For a graph $G$ with $p$ vertices the closed convex cone ${\mathbb{S}}_{⪰0}^p(G)$ consists of all real positive semidefinite $p\times p$ matrices with zeros in the off-diagonal…