“…In recent years, many authors pay more attention to preconditioned iterative methods [7][8][9][10][15][16][17][18][19][20]34,35] for solving large sparse linear systems in terms of lower requirement for storage and fast convergence. A large amount of work has been devoted to studying preconditioners, such as, block diagonal preconditioner (BD) [12,13], block triangular preconditioner (BT) [11,14,22,23,25] , constraint preconditioner (CP) [21,24,[26][27][28] and product preconditioner (PP) [23,29].…”