ELA ON THE MAXIMAL ANGLE BETWEEN COPOSITIVE MATRICES∗

Abstract. Hiriart-Urruty and Seeger have posed the problem of finding the maximal possible angle θmax(Cn) between two copositive matrices of order n [J.-B. Hiriart-Urruty and A. Seeger. A variational approach to copositive matrices. SIAM Rev., 52:593–629, 2010.]. They have proved that θmax(C2) = 3 4 pi and conjectured that θmax(Cn) is equal t