@article{CMJ_2009__59_1_a15,
     author = {Bebiano, N. and Provid\^encia, J. da and Teixeira, R.},
     title = {Indefinite numerical range of $3\times 3$ matrices},
     journal = {Czechoslovak Mathematical Journal},
     pages = {221--239},
     publisher = {mathdoc},
     volume = {59},
     number = {1},
     year = {2009},
     mrnumber = {2486627},
     zbl = {1224.15043},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMJ_2009__59_1_a15/}
}