@article {GolubGreifVarah2005, AUTHOR = {Golub, Gene H. and Greif, Chen and Varah, James M.}, TITLE = {An algebraic analysis of block diagonal preconditioner for saddle point systems}, JOURNAL = {SIAM J. Matrix Anal. Appl.}, VOLUME = {27}, YEAR = {2005}, NUMBER = {3} PAGES = {779--792} }