“…For some problems, especially those arising in constrained optimization and in mixed finite element discretization of the linearized Navier-Stokes equations [1,9], C = B and D = 0. For others, such as those arising from stabilized finite elements [4,9,21,[26][27][28], C = B, D = 0 but D is small. In addition, if one uses spectral (Chebyshev collocation) approach to discretize, for example, the Stokes equations, then one has a (generalized) saddle point system with C = B was considered by Murphy et al [19].…”