Vol. 53, No. 2, 1974

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The norm of a certain derivation

Charles Alan McCarthy

Vol. 53 (1974), No. 2, 515–518
Abstract

J. C. Stampfli has asked whether the norm of the derivation QT : A TA AT as a mapping of the subalgebra A of B(H) into B(H) is given by inf{2T A′∥ : A′∈ A′}. That this need not be the case is shown through an example in 4 × 4 matrices.

Mathematical Subject Classification 2000
Primary: 46L05
Secondary: 47B47
Milestones
Received: 2 May 1973
Published: 1 August 1974
Authors
Charles Alan McCarthy