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On the ellipticity of the higher rank numerical range
N. Bebiano, R. Lemos, G. Soares·December 2, 2025·DOI: 10.1016/j.jmaa.2026.130614
Mathematics
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Abstract
The higher rank numerical range is a concept that generalizes the classical numerical range, and it has application in quantum error correction. We investigate these sets for $2$-by-$2$ block matrices with associated Kippenhahn curves consisting of ellipses (and eventually points). As a consequence, elliptical higher rank numerical range results are derived in a unified way, using an approach developed by Spitkovsky {\it et al}.