MAPPING PRESERVING NUMERICAL RANGE OF OPERATOR PRODUCTS ON C∗-ALGEBRAS
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초록
Let A and B be two unital C∗-algebras. Denote by W(a) the numerical range of an element a ∈ A. We show that the condition W(ax) = W(bx), ∀x ∈ A implies that a = b. Using this, among other results, it is proved that if Φ : A → B is a surjective map such that W(Φ (a)Φ (b)Φ (c)) = W(abc) for all a, b and c ∈ A, then Φ (1) ∈ Z(B) and the map ψ = Φ (1)2Φ is multiplicative.
Abstract
Let A and B be two unital C∗-algebras. Denote by W(a) the numerical range of an element a ∈ A. We show that the condition W(ax) = W(bx), ∀x ∈ A implies that a = b. Using this, among other results, it is proved that if Φ : A → B is a surjective map such that W(Φ (a)Φ (b)Φ (c)) = W(abc) for all a, b and c ∈ A, then Φ (1) ∈ Z(B) and the map ψ = Φ (1)2Φ is multiplicative.
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