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math.FA2026
On circular Kippenhahn curves and the Gau-Wang-Wu conjecture about nilpotent partial isometries
Eric Shen
We study linear operators on a finite-dimensional space whose Kippenhahn curves consist of concentric circles centered at the origin. We say that such operators have Circularity pr…
math.FA2026
On Kippenhahn curves of low rank partial isometries
Nikita Popov, Eric Shen, Ilya M. Spitkovsky
Conditions are established for rank three partial isometries to have circular components contained in their Kippenhahn curves. In particular, such matrices with circular numerical…