@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/