“…In the past few years, much work also has been devoted to developing efficient preconditioners for saddle point problems. A variety of preconditioners have been proposed and studied in many papers, such as block diagonal and block triangular preconditioners [7,19,20,24], constraint preconditioners [8,25], HSS-based preconditioners [3,6,12,13,30], dimensional split preconditioners [15,16], H−matrix preconditioners [17] and so on. In [14], Benzi, Golub and Liesen discussed a selection of numerical methods and useful preconditioners for saddle point problems.…”