Displaying similar documents to “Extreme points of the closed unit ball in C*-algebras”

On a general bidimensional extrapolation problem

Rodrigo Arocena, Fernando Montana (1993)

Colloquium Mathematicae

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Several generalized moment problems in two dimensions are particular cases of the general problem of giving conditions that ensure that two isometries, with domains and ranges contained in the same Hilbert space, have commutative unitary extensions to a space that contains the given one. Some results concerning this problem are presented and applied to the extension of functions of positive type.

On unitary convex decompositions of vectors in a J B * -algebra

Akhlaq A. Siddiqui (2013)

Archivum Mathematicum

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By exploiting his recent results, the author further investigates the extent to which variation in the coefficients of a unitary convex decomposition of a vector in a unital J B * -algebra permits the vector decomposable as convex combination of fewer unitaries; certain C * -algebra results due to M. Rørdam have been extended to the general setting of J B * -algebras.

Representing measures for the disc algebra and for the ball algebra

Raymond Brummelhuis, Jan Wiegerinck (1991)

Annales Polonici Mathematici

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We consider the set of representing measures at 0 for the disc and the ball algebra. The structure of the extreme elements of these sets is investigated. We give particular attention to representing measures for the 2-ball algebra which arise by lifting representing measures for the disc algebra.