@article{GDZPPN001173022, title = {A Symmetric Numerical Range for Matrices.}, journal = {Numerische Mathematik}, volume = {26}, year = {1976}, pages = {99-106}, zbl = {0312.65034}, url = {http://dml.mathdoc.fr/item/GDZPPN001173022} }
Schneider, H.; Saunders, B.D. A Symmetric Numerical Range for Matrices.. Numerische Mathematik, Tome 26 (1976) pp. 99-106. http://gdmltest.u-ga.fr/item/GDZPPN001173022/