@article {GreifOverton2010,
    AUTHOR = {Greif, Chen and Overton, Michael L.},
     TITLE = {An analysis of low-rank modifications of preconditioners for
              saddle point systems},
   JOURNAL = {Electron. Trans. Numer. Anal.},
    VOLUME = {37},
      YEAR = {2010},
     PAGES = {307--320} 
}