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Transitivity for linear operators on a Banach space

Bertram Yood (1999)

Studia Mathematica

Let G be the multiplicative group of invertible elements of E(X), the algebra of all bounded linear operators on a Banach space X. In 1945 Mackey showed that if x 1 , , x n and y 1 , , y n are any two sets of linearly independent elements of X with the same number of items, then there exists T ∈ G so that T ( x k ) = y k , k = 1 , , n . We prove that some proper multiplicative subgroups of G have this property.

Transitivity of proximinality and norm attaining functionals

Darapaneni Narayana, T. S. S. R. K. Rao (2006)

Colloquium Mathematicae

We study the question of when the set of norm attaining functionals on a Banach space is a linear space. We show that this property is preserved by factor reflexive proximinal subspaces in R ( 1 ) ˜ spaces and generally by taking quotients by proximinal subspaces. We show, for (ℓ₂) and c₀-direct sums of families of reflexive spaces, the transitivity of proximinality for factor reflexive subspaces. We also investigate the linear structure of the set of norm attaining functionals on hyperplanes of c₀ and...

Translation-invariant operators on Lorentz spaces L(1,q) with 0 < q < 1

Leonardo Colzani, Peter Sjögren (1999)

Studia Mathematica

We study convolution operators bounded on the non-normable Lorentz spaces L 1 , q of the real line and the torus. Here 0 < q < 1. On the real line, such an operator is given by convolution with a discrete measure, but on the torus a convolutor can also be an integrable function. We then give some necessary and some sufficient conditions for a measure or a function to be a convolutor on L 1 , q . In particular, when the positions of the atoms of a discrete measure are linearly independent over the rationals,...

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