“…The system (1.1) arises from many areas of computational sciences and engineerings, for example, in certain finite element and finite difference discretization of Navier-Stokes equations, Oseen equations, and mixed finite element discretization of second order convection-diffusion problems (cf. [3,8,13,14,16,18,19]). For the saddle point problem, there exist many algorithms, for example, the Krylov iteration methods with block diagonal, triangular block or constraint preconditioners (see [3] and the references therein).…”