Operators and Matrices · Volume 5, Issue 1 Multiplicities, boundary points, and {joint} numerical ranges 05-02 Pages 41-52 DOI 10.7153/oam-05-02 Downloads Short PDF Full PDF PNG Authors Wai-Shun Cheung Xuhua Liu Tin-Yau Tam Keywords joint numerical range multiplicity extreme point sharp point boundary point Subject classes 15A60