In this paper we study $ A $-projections, ie operators of a Hilbert space $\HH $ which act as
projections when a seminorm is considered in $\HH $. $ A $-projections were introduced by …

In a recent article, Smale and Zhou define a notion of rich data for sampling problems and
reconstruction of signals from a discrete set of samples and study different least-square …

SARD’S APPROXIMATION PROCESSES AND OBLIQUE PROJECTIONS 1. Introduction In
1950, Arthur Sard [17] proposed an operator theoreti Page 1 SARD’S APPROXIMATION …

We obtain a condition implying that the union of two frame sequences is also a frame
sequence. Christensen found a condition for this in terms of orthogonal projections. We …

A finitely generated shift invariant space V is a closed subspace of L 2 (R d) that can be
generated by the integer translates of a finite number of functions. A set of frame generators …

Multiplicatively invariant (MI) spaces are closed subspaces of $ L^ 2 (\Omega,\mathcal {H}) $
that are invariant under multiplications of (some) functions in $ L^{\infty}(\Omega) $. In this …

En esta tesis se presentan los resultados obtenidos en los problemas que derivaron del
estudio del problema de recuperación de fase. En primer lugar, se estudian relaciones entre …

Let $\mathcal {E} $ be a Banach space contained in a Hilbert space $\mathcal {L} $. Assume
that the inclusion is continuous with dense range. Following the terminology of Gohberg and …

Los espacios invariantes por traslaciones son espacios cerrados de L2 (Rd) que son
invariantes por traslaciones enteras. Estos espacios juegan un rol muy importante en teorıa …

El trabajo se encuentra organizado del siguiente modo: en los capítulos 1, 2 y 3 se
desarrollan los preliminares necesarios para los desarrollos posteriores mientras que en los …