Abstract.
Let \( \mathcal P \) be the interior of a parabola of the complex plane. We show that, for all operators with numerical range contained in \( \mathcal P \) , \( \mathcal P \) is a 5-spectral set.
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Received: 22 July 2003; revised manuscript accepted: 15 December 2003
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Crouzeix, M. Operators with numerical range in a parabola. Arch. Math. 82, 517–527 (2004). https://doi.org/10.1007/s00013-004-0605-2
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DOI: https://doi.org/10.1007/s00013-004-0605-2