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Given an r × r complex matrix T , if T = U |T | is the polar decomposition of T , then, the Aluthge transform is defined by ∆ (T ) = |T |U |T |. Let ∆n(T ) denote the n-times iterated Aluthge transform of T , i.e. ∆0(T ) = T and ∆n(T ) = ∆(∆n−1(T )), n ∈ N. We prove that the sequence {∆n(T )}n∈N converges for every r× r diagonalizable matrix T . We show… (More)

Given an r × r complex matrix T , if T = U |T | is the polar decomposition of T , then, the Aluthge transform is defined by ∆ (T ) = |T |U |T |. Let ∆n(T ) denote the n-times iterated Aluthge transform of T , i.e. ∆0(T ) = T and ∆n(T ) = ∆(∆n−1(T )), n ∈ N. We prove that the sequence {∆n(T )}n∈N converges for every r × r matrix T . This result was… (More)

In this paper we study shorted operators relative to two different subspaces, for bounded operators on infinite dimensional Hilbert spaces. We define two notions of “complementability” in the sense of Ando for operators, and study the properties of the shorted operators when they can be defined. We use these facts in order to define and study the notions of… (More)

Let H be a (separable) Hilbert space and {ek}k≥1 a fixed orthonormal basis of H. Motivated by many papers on scaled projections, angles of subspaces and oblique projections, we define and study the notion of compatibility between a subspace and the abelian algebra of diagonal operators in the given basis. This is used to refine previous work on scaled… (More)

- Elona Agora, Jorge Antezana, María J. Carro, Javier Soria
- J. London Math. Society
- 2014

We prove the Lorentz-Shimogaki and Boyd theorems for the spaces Λu(w). As a consequence, we give the complete characterization of the strong boundedness of H on these spaces in terms of some geometric conditions on the weights u and w, whenever p > 1. For these values of p, we also give the complete solution of the weak-type boundedness of the… (More)

Given a n × n positive semidefinite matrix A and a subspace S of C, Σ(S, A) denotes the shorted matrix of A to S. We consider the notion of spectral shorted matrix ρ(S, A) = lim m→∞ Σ(S, A). We completely characterize this matrix in terms of S and the spectrum and the eigenspaces of A. We show the relation of this notion with the spectral order of matrices… (More)

IfH is a Hilbert space, S ⊆ H is a closed subspace of H, and A is a positive bounded linear operator on H, the spectral shorted operator ρ(S, A) is defined as the infimum of the sequence Σ(S, An)1/n, where Σ(S, B) denotes the shorted operator of B to S. We characterize the left spectral resolution of ρ(S, A) and show several properties of this operator,… (More)

- JORGE ANTEZANA, ENRIQUE R. PUJALS, DEMETRIO STOJANOFF, Mischa Cotlar
- 2008

Given an r × r complex matrix T , if T = U |T | is the polar decomposition of T , then the Aluthge transform is defined by ∆ (T ) = |T |U |T |. Let ∆n(T ) denote the n-times iterated Aluthge transform of T , i.e. ∆0(T ) = T and ∆n(T ) = ∆(∆n−1(T )), n ∈ N. In this paper we make a brief survey on the known properties and applications of the Aluthge… (More)

Let λ ∈ (0, 1) and let T be a r × r complex matrix with polar decomposition T = U |T |. Then, the λAluthge transform is defined by ∆λ (T ) = |T | U |T |. Let ∆nλ(T ) denote the n-times iterated Aluthge transform of T , n ∈ N. We prove that the sequence {∆nλ(T )}n∈N converges for every r × r diagonalizable matrix T . We show regularity results for the two… (More)

- Jorge Antezana, Eduardo Chiumiento
- 2016

We solve the problem of best approximation by partial isometries of given rank to an arbitrary rectangular matrix, when the distance is measured in any unitarily invariant norm. In the case where the norm is strictly convex, we parametrize all the solutions. In particular, this allow us to give a simple necessary and sufficient condition for uniqueness. We… (More)