@article{ELA_2005__13__a21,
     author = {Hartwig, Robert E. and Maroulas, John},
     title = {Focal power},
     journal = {The electronic journal of linear algebra},
     pages = {56--71},
     publisher = {mathdoc},
     volume = {13},
     year = {2005},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/ELA_2005__13__a21/}
}