Displaying similar documents to “Unitary extensions of isometries, generalized interpolation and band extensions”

On a general bidimensional extrapolation problem

Rodrigo Arocena, Fernando Montana (1993)

Colloquium Mathematicae

Similarity:

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.

Unitary asymptotes of Hilbert space operators

László Kérchy (1994)

Banach Center Publications

Similarity:

In this survey article we are going to present the effectiveness of the use of unitary asymptotes in the study of Hilbert space operators.

The range of a contractive projection in L(H).

Yves Raynaud (2004)

Revista Matemática Complutense

Similarity:

We show that the range of a contractive projection on a Lebesgue-Bochner space of Hilbert valued functions L(H) is isometric to a l-direct sum of Hilbert-valued L-spaces. We explicit the structure of contractive projections. As a consequence for every 1 < p < ∞ the class C of l-direct sums of Hilbert-valued L-spaces is axiomatizable (in the class of all Banach spaces).

Extreme points of the closed unit ball in C*-algebras

Rainer Berntzen (1997)

Colloquium Mathematicae

Similarity:

In this short note we give a short and elementary proof of a characterization of those extreme points of the closed unit ball in C*-algebras which are unitary. The result was originally proved by G. K. Pedersen using some methods from the theory of approximation by invertible elements.

Some invariant subspaces for A-contractions and applications

Laurian Suciu (2006)

Extracta Mathematicae

Similarity:

Some invariant subspaces for the operators A and T acting on a Hilbert space H and satisfying T*AT ≤ A and A ≥ 0, are presented. Especially, the largest invariant subspace for A and T on which the equality T* AT = A occurs, is studied in connections to others invariant or reducing subspaces for A, or T. Such subspaces are related to the asymptotic form of the subspace quoted above, this form being obtained using the operator limit of the sequence {TAT; n ≥ 1}. More complete results are...