Hai-yan Zhang, Yan-Ni Dou, Mei-Feng Wang, Hong-ke Du. On the boundary of numerical ranges of operators. Appl. Math. Lett., 24(5):620-622, 2011. [doi]
@article{ZhangDWD11, title = {On the boundary of numerical ranges of operators}, author = {Hai-yan Zhang and Yan-Ni Dou and Mei-Feng Wang and Hong-ke Du}, year = {2011}, doi = {10.1016/j.aml.2010.11.024}, url = {https://doi.org/10.1016/j.aml.2010.11.024}, researchr = {https://researchr.org/publication/ZhangDWD11}, cites = {0}, citedby = {0}, journal = {Appl. Math. Lett.}, volume = {24}, number = {5}, pages = {620-622}, }