“…In practice, this means that we need to solve the correction equation, i.e., the equation which updates the current approximate eigenvector, in a subspace that is orthogonal to the most current approximate eigenvectors. Several methods can be mentioned including the Trace Minimization method [12,11], the Davidson method [4,9] and the Jacobi-Davidson approach [14,13,16]. Most of these methods update an existing approximation by a step of Newton's method and this was illustrated in a number of papers, see, e.g., [8], and in [17].…”