More on extremal positive semidefinite doubly stochastic matrices

AbstractLet Kn be the convex set of n×n positive semidefinite doubly stochastic matrices. We show that for matrices with a special type of graph extremality can be determined by graph and rank. We also give a complete classification of the extreme matrices in K5, and in particular give examples of two matrices in K5 with the same graph and rank, one extreme and one not