Extremals and exposed faces of the cone of positive maps
David A. Yopp, Richard D. Hill § · Linear and Multilinear Algebra · 2005
We show that for a matrix A of size n × m, the maps are extremals of the cone of positive maps acting . When the rank of A equals 1 or m (in which case, necessarily m ≤ n), we show that these extremals are exposed.