@article{1077465062, author = {Hoffman, A. J. and Wielandt, H. W.}, title = {The variation of the spectrum of a normal matrix}, journal = {Duke Math. J.}, volume = {20}, number = {1}, year = {1953}, pages = { 37-39}, language = {en}, url = {http://dml.mathdoc.fr/item/1077465062} }
Hoffman, A. J.; Wielandt, H. W. The variation of the spectrum of a normal matrix. Duke Math. J., Tome 20 (1953) no. 1, pp. 37-39. http://gdmltest.u-ga.fr/item/1077465062/