TY - JOUR T1 - Block preconditioners based on approximate commutators JF - SIAM Journal on Scientific Computing Y1 - 2006 A1 - Elman, Howard A1 - Howle, V. E A1 - Shadid, J. A1 - Shuttleworth, R. A1 - Tuminaro, R. VL - 27 CP - 5 ER -