@article{10_4153_CMB_2000_053_3,
     author = {Li, Chi-Kwong and Zaharia, Alexandru},
     title = {Nonconvexity of the {Generalized} {Numerical} {Range} {Associated} with the {Principal} {Character}},
     journal = {Canadian mathematical bulletin},
     pages = {448--458},
     year = {2000},
     volume = {43},
     number = {4},
     doi = {10.4153/CMB-2000-053-3},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-2000-053-3/}
}