@article{ELA_2008__17__a30,
     author = {Bebiano, Natalia and da Provid\^encia, Joao and Nata, Ana Cristina and da Graca Pereira Soares, Maria},
     title = {Krein spaces numerical ranges and their computer generation},
     journal = {The electronic journal of linear algebra},
     pages = {192--208},
     publisher = {mathdoc},
     volume = {17},
     year = {2008},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/ELA_2008__17__a30/}
}