“…Such problems arise in many applications (see e.g., [35,41,47]) and, perhaps more importantly, they arise as subproblems in Newton-type or sequential quadratic programming (SQP) methods for many nonlinear elliptic control problems (see, e.g., [9,18,33,34,43]). After a discretization, a linear-quadratic elliptic optimal control problems leads to a large-scale quadratic programming problems whose solution is, under suitable conditions, characterized through the linear system of optimality conditions.…”