M. Ptak

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math.FA2026

Unitarily invariant norms

Stephan Ramon Garcia, Javad Mashreghi, Marek Ptak +1

This survey paper provides a comprehensive study of unitarily invariant norms on the algebra of $n \times n$ matrices. This investigation leads naturally to the theory of symmetric…

math.FA2024

Conjugations of Unitary Operators, II

Javad Mashreghi, Marek Ptak, William T. Ross

For a given unitary operator $U$ on a separable complex Hilbert space $\h$, we describe the set $C_{c} (U)$ of all conjugations $C$ (antilinear, isometric, and involutive…

math.FA2024

Conjugations of Unitary operators, I

Javad Mashreghi, Marek Ptak, William T. Ross

If $U$ is a unitary operator on a separable complex Hilbert space $H$ , an application of the spectral theorem says there is a conjugation $C$ on $H$ (an antilin…