@article{ZHo08,
    AUTHOR = {Zachlin, Paul F. and Hochstenbach, Michiel E.},
     TITLE = {On the numerical range of a matrix},
   JOURNAL = {Linear Multilinear Algebra},
  FJOURNAL = {Linear and Multilinear Algebra},
    VOLUME = {56},
      YEAR = {2008},
    NUMBER = {1-2},
     PAGES = {193--228},
      ISSN = {0308-1087},
   MRCLASS = {47A12, 15A60, 15A33},
      NOTE = {English translation with comments and corrections of a paper by Rudolph Kippenhahn}
}