Using copositivity for global optimality criteria in concave quadratic programming problems

In this note the authors specify a necessary and sufficient condition for global optimality in concave quadratic minimization problems. Using this condition, it follows that, from the perspective of worst-case complexity of concave quadratic problems, the difference between local and global optimality conditions is not as large as in general. As an essential ingredient, the authors here use the •-subdifferential calculus via an approach of Hiriart-Urruty and Lemarechal.