@article{CMUC_1976__17_2_a5,
     author = {Pt\'ak, Vlastimil},
     title = {The spectral radii of an operator and its modulus},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {273--279},
     publisher = {mathdoc},
     volume = {17},
     number = {2},
     year = {1976},
     mrnumber = {0410416},
     zbl = {0332.15003},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_1976__17_2_a5/}
}