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In mathematics, especially operator theory, a convexoid operator is a bounded linear operator T on a complex Hilbert space H such that the closure of the numerical range coincides with the convex hull of its spectrum.

An example of such an operator is a normal operator (or some of its generalization).

A closely related operator is a spectraloid operator: an operator whose spectral radius coincides with its numerical radius. In fact, an operator T is convexoid if and only if \( {\displaystyle T-\lambda } \) is spectraloid for every complex number\( \lambda \).
See also

Aluthge transform

References

T. Furuta. Certain convexoid operators

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