@article{ELA_2008__17__a15,
     author = {Friedland, Shmuel and Virnik, Elena},
     title = {Nonnegativity of {Schur} complements of nonnegative idempotent matrices},
     journal = {The electronic journal of linear algebra},
     pages = {426--435},
     publisher = {mathdoc},
     volume = {17},
     year = {2008},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/ELA_2008__17__a15/}
}