“…Linear systems of the type (1) will be referred to as (generalized) "saddle point systems with indefinite (1, 1) block." Such linear systems arise in various areas of scientific computing, including the solution of eigenvalue problems in fluid mechanics [8,13] and electromagnetics [2] by shift-and-invert algorithms, and in certain time-harmonic wave propagation problems [12,15]. We emphasize that while numerous effective solution algorithms exist for the case of a positive definite or semidefinite (1, 1) block (corresponding to either β ≤ 0 or β > 0 but smaller than the real part of the eigenvalue of A of smallest magnitude), see [3,7,9], relatively little has been done for the case where the (1, 1) block is indefinite.…”