On a conjecture of Hubner

  • F. O. Farid


In this paper we show that for a bounded linear operatorA on a complex Hilbert spaceH, the points on the boundary of the numerical range ofA with infinite curvature and unique tangent are in the essential spectrum ofA, thus positively answering a conjecture raised by Hubner in [3].


Spectrum numerical range Hilbert space 


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Copyright information

© Indian Academy of Sciences 1999

Authors and Affiliations

  • F. O. Farid
    • 1
  1. 1.VeraonCanada

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