engleski

Roberts orthogonality and Davis–Wielandt shell

Let A be a unital C*-algebra with the unit e. We consider the elements a in A which are Roberts orthogonal to the unit e. We obtain a characterization of this orthogonality in terms of the Davis–Wielandt shell of a and show that, for certain classes of elements of A, the Roberts orthogonality of a and e is equivalent to the symmetry of the numerical range of a with respect to the origin.

Roberts orthogonality ; Numerical range ; Davis–Wielandt shell ; C*-algebra

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