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 ${\displaystyle \lambda }$.

See also

• Aluthge transform

References

• T. Furuta. Certain convexoid operators