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An approximation problem in multiplicatively invariant spaces
(American Mathematical Society, 2017-07)
Let H be Hilbert space and (Ω, m) a σ-finite measure space. Multiplicatively invariant(MI) spaces are closed subspaces of L2(Ω, H) that are invariant under point-wise multiplication byfunctions from a fixed subset of L∞(Ω). ...
Approximation by group invariant subspaces
(Gauthier-Villars/Editions Elsevier, 2020-10)
In this article we study the structure of Γ-invariant spaces of L2(S). Here S is a second countable LCA group. The invariance is with respect to the action of Γ, a non commutative group in the form of a semidirect product ...
Weak-field approximation of effective gravitational theory with local Galilean invariance
(Elsevier B.V., 2009-09-14)
We examine the weak-field approximation of locally Galilean invariant gravitational theories with general covariance in a (4 + 1)-dimensional Galilean framework. The additional degrees of freedom allow us to obtain Poisson, ...
Weak-field approximation of effective gravitational theory with local Galilean invariance
(Elsevier B.V., 2009-09-14)
We examine the weak-field approximation of locally Galilean invariant gravitational theories with general covariance in a (4 + 1)-dimensional Galilean framework. The additional degrees of freedom allow us to obtain Poisson, ...
Subspaces with extra invariance nearest to observed data
(Elsevier Inc, 2016-09)
Given an arbitrary finite set of data F = {f1, ..., fm} ⊂ L2(Rd) we prove the existence and show how to construct a “small shift invariant space” that is “closest” to the data F over certain class of closed subspaces of ...
Approximation by partial isometries and symmetric approximation of finite frames
(Birkhauser Boston Inc, 2018-08)
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, ...