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## ‣ Sparsity Equivalence of Anisotropic Decompositions

Kutyniok, Gitta
Tipo: Artigo de Revista Científica
Publicado em 19/01/2011 Português
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Anisotropic decompositions using representation systems such as curvelets, contourlet, or shearlets have recently attracted significantly increased attention due to the fact that they were shown to provide optimally sparse approximations of functions exhibiting singularities on lower dimensional embedded manifolds. The literature now contains various direct proofs of this fact and of related sparse approximation results. However, it seems quite cumbersome to prove such a canon of results for each system separately, while many of the systems exhibit certain similarities. In this paper, with the introduction of the concept of sparsity equivalence, we aim to provide a framework which allows categorization of the ability for sparse approximations of representation systems. This framework, in particular, enables transferring results on sparse approximations from one system to another. We demonstrate this concept for the example of curvelets and shearlets, and discuss how this viewpoint immediately leads to novel results for both systems.; Comment: 20 pages, 4 figures

## ‣ Generalized low-pass filters and multiresolution analyses

Baggett, Lawrence W.; Furst, Veronika; Merrill, Kathy D.; Packer, Judith A.
Tipo: Artigo de Revista Científica
Publicado em 10/12/2008 Português
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We study generalized filters that are associated to multiplicity functions and homomorphisms of the dual of an abelian group. These notions are based on the structure of generalized multiresolution analyses. We investigate when the Ruelle operator corresponding to such a filter is a pure isometry, and then use that characterization to study the problem of when a collection of closed subspaces, which satisfies all the conditions of a GMRA except the trivial intersection condition, must in fact have a trivial intersection. In this context, we obtain a generalization of a theorem of Bownik and Rzeszotnik.; Comment: 20 pages including bibliography

## ‣ Multidimensional Tauberian theorems for wavelet and non-wavelet transforms

Pilipović, Stevan; Vindas, Jasson
Tipo: Artigo de Revista Científica
Português
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We study several Tauberian properties of regularizing transforms of tempered distributions with values in Banach spaces, that is, transforms of the form $M^{\mathbf{f}}_{\phi}(x,y)=(\mathbf{f}\ast\phi_{y})(x)$, where the kernel $\phi$ is a test function and $\phi_{y}(\cdot)=y^{-n}\phi(\cdot/y)$. If the zeroth moment of $\phi$ vanishes, it is a wavelet type transform; otherwise, we say it is a non-wavelet type transform. The first aim of this work is to show that the scaling (weak) asymptotic properties of distributions are \emph{completely} determined by boundary asymptotics of the regularizing transform plus natural Tauberian hypotheses. Our second goal is to characterize the spaces of Banach space-valued tempered distributions in terms of the transform $M^{\mathbf{f}}_{\phi}(x,y)$. We investigate conditions which ensure that a distribution that a priori takes values in locally convex space actually takes values in a narrower Banach space. Special attention is paid to find the \emph{optimal} class of kernels $\phi$ for which these Tauberian results hold. We give various applications of our Tauberian theory in the pointwise and (micro-)local regularity analysis of Banach space-valued distributions, and develop a number of techniques which are specially useful when applied to scalar-valued functions and distributions. Among such applications...

## ‣ Implementation of discretized Gabor frames and their duals

Kloos, Tobias; Stöckler, Joachim; Gröchenig, Karlheinz
Tipo: Artigo de Revista Científica
Publicado em 23/06/2015 Português
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The usefulness of Gabor frames depends on the easy computability of a suitable dual window. This question is addressed under several aspects: several versions of Schulz's iterative algorithm for the approximation of the canonical dual window are analyzed for their numerical stability. For Gabor frames with totally positive windows or with exponential B-splines a direct algorithm yields a family of exact dual windows with compact support. It is shown that these dual windows converge exponentially fast to the canonical dual window.; Comment: 16 pages, 4 figures

## ‣ Stability Criterion for Convolution-Dominated Infinite Matrices

Sun, Qiyu
Tipo: Artigo de Revista Científica
Publicado em 22/07/2009 Português
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Let $\ell^p$ be the space of all $p$-summable sequences on $\mathbb{Z}$. An infinite matrix is said to have $\ell^p$-stability if it is bounded and has bounded inverse on $\ell^p$. In this paper, a practical criterion is established for the $\ell^p$-stability of convolution-dominated infinite matrices.

## ‣ Decompositions of Trigonometric Polynomials with Applications to Multivariate Subdivision Schemes

Dyn, Nira; Skopina, Maria
Tipo: Artigo de Revista Científica
Publicado em 24/07/2009 Português
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We study multivariate trigonometric polynomials, satisfying a set of constraints close to the known Strung-Fix conditions. Based on the polyphase representation of these polynomials relative to a general dilation matrix, we develop a simple constructive method for a special type of decomposition of such polynomials. These decompositions are of interest to the analysis of convergence and smoothness of multivariate subdivision schemes associated with general dilation matrices. We apply these decompositions, by verifying sufficient conditions for the convergence and smoothness of multivariate scalar subdivision schemes, proved here. For the convergence analysis our sufficient conditions apply to arbitrary dilation matrices, while the previously known necessary and sufficient conditions are relevant only in case of dilation matrices with a self similar tiling. For the analysis of smoothness, we state and prove two theorems on multivariate matrix subdivision schemes, which lead to sufficient conditions for C^1 limits of scalar multivariate subdivision schemes associated with isotropic dilation matrices. Although similar results are stated in the literature, we give here detailed proofs of the results, which we could not find elsewhere.; Comment: 30 pages

## ‣ A duality approach to representations of Baumslag-Solitar groups

Dutkay, Dorin Ervin; Jorgensen, Palle E. T.
Tipo: Artigo de Revista Científica
Português
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We give an operator theoretic approach to the constructions of multiresolutions as they are used in a number of basis constructions with wavelets, and in Hilbert spaces on fractals. Our approach starts with the following version of the classical Baumslag-Solitar relations $u t = t^2 u$ where $t$ is a unitary operator in a Hilbert space $\mathcal H$ and $u$ is an isometry in $\mathcal H$. There are isometric dilations of this system into a bigger Hilbert space, relevant for wavelets. For a variety of carefully selected dilations, the bigger'' Hilbert space may be $L^2(\br)$, and the dilated operators may be the unitary operators which define a dyadic wavelet multiresolutions of $L^2(\br)$ with the subspace $\mathcal H$ serving as the corresponding resolution subspace. That is, the initialized resolution which is generated by the wavelet scaling function(s). In the dilated Hilbert space, the Baumslag-Solitar relations then take the more familiar form $u t u^{-1} = t^2$. We offer an operator theoretic framework including the standard construction; and we show how the representations of certain discrete semidirect group products serve to classify the possibilities. For this we analyze and compare several types of unitary representations of these semidirect products: the induced representations in Mackey's theory...

## ‣ Multivariate Wavelet Frames

Skopina, M.
Tipo: Artigo de Revista Científica
Publicado em 18/04/2007 Português
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We proved that for any matrix dilation and for any positive integer $n$, there exists a compactly supported tight wavelet frame with approximation order $n$. Explicit methods for construction of dual and tight wavelet frames with a given number of vanishing moments are suggested.; Comment: LaTex file, 28 pages

## ‣ Shear Anisotropic Inhomogeneous Besov And Triebel-Lizorkin Spaces In $R^d$

Vera, Daniel
Tipo: Artigo de Revista Científica
Publicado em 03/11/2012 Português
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We define distribution spaces of a sequence of convolutions of a set of distributions with smooth functions, the shearlet system. Then, we define associated sequence spaces and prove characterizations. We also show a reproducing identity in the class of distributions. Finally, we prove Sobolev-type embeddings within the shear anisotropic inhomogeneous spaces and embeddings between (classical dyadic) isotropic inhomogeneous spaces and shear anisotropic inhomogeneous spaces.; Comment: 36 pages. arXiv admin note: substantial text overlap with arXiv:1203.5136

## ‣ Surgery of spline-type and molecular frames

Romero, José Luis
Tipo: Artigo de Revista Científica
Português
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We prove a result about producing new frames for general spline-type spaces by piecing together portions of known frames. Using spline-type spaces as models for the range of certain integral transforms, we obtain results for time-frequency decompositions and sampling.; Comment: 34 pages. Corrected typos

## ‣ Convergence rate of wavelet expansions of Gaussian random processes

Olenko, Andriy; Kozachenko, Yuriy; Polosmak, Olga
Tipo: Artigo de Revista Científica
Publicado em 07/08/2013 Português
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The paper characterizes uniform convergence rate for general classes of wavelet expansions of stationary Gaussian random processes. The convergence in probability is considered.; Comment: This is an Author's Accepted Manuscript of an article to be published in the Communications in Statistics - Theory and Methods. 24 pages. arXiv admin note: substantial text overlap with arXiv:1307.2428

## ‣ Uniform convergence of compactly supported wavelet expansions of Gaussian random processes

Kozachenko, Yuriy; Olenko, Andriy; Polosmak, Olga
Tipo: Artigo de Revista Científica
Publicado em 07/08/2013 Português
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New results on uniform convergence in probability for expansions of Gaussian random processes using compactly supported wavelets are given. The main result is valid for general classes of nonstationary processes. An application of the obtained results to stationary processes is also presented. It is shown that the convergence rate of the expansions is exponential.; Comment: This is an Author's Accepted Manuscript of an article published in the Communications in Statistics - Theory and Methods. 15 pages

## ‣ Bernuau spline wavelets and Sturmian sequences

Andrle, Miroslav; Burdik, Cestmir; Gazeau, Jean-Pierre
Tipo: Artigo de Revista Científica
Publicado em 24/09/2003 Português
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A spline wavelets construction of class C^n(R) supported by sequences of aperiodic discretizations of R is presented. The construction is based on multiresolution analysis recently elaborated by G. Bernuau. At a given scale, we consider discretizations that are sets of left-hand ends of tiles in a self-similar tiling of the real line with finite local complexity. Corresponding tilings are determined by two-letter Sturmian substitution sequences. We illustrate the construction with examples having quadratic Pisot-Vijayaraghavan units (like tau = (1 + sqrt{5})/2 or tau^2 = (3 + sqrt{5})/2) as scaling factor. In particular, we present a comprehensive analysis of the Fibonacci chain and give the analytic form of related scaling functions and wavelets as splines of second order. We also give some hints for the construction of multidimensional spline wavelets based on stone-inflation tilings in arbitrary dimension.; Comment: 41 pages,10 figures

## ‣ Random Wavelet Series: Theory and Applications

Aubry, Jean-Marie; Jaffard, Stéphane
Tipo: Artigo de Revista Científica
Publicado em 28/10/2003 Português
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Random Wavelet Series form a class of random processes with multifractal properties. We give three applications of this construction. First, we synthesize a random function having any given spectrum of singularities satisfying some conditions (but including non-concave spectra). Second, these processes provide examples where the multifractal spectrum coincides with the spectrum of large deviations, and we show how to recover it numerically. Finally, particular cases of these processes satisfy a generalized selfsimilarity relation proposed in the theory of fully developed turbulence.; Comment: To appear in Annales Math\'ematiques Blaise Pascal

## ‣ Sampling theorems on locally compact groups from oscillation estimates

Fuehr, Hartmut; Groechenig, Karlheinz
Tipo: Artigo de Revista Científica
Publicado em 08/09/2005 Português
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We present a general approach to derive sampling theorems on locally compact groups from oscillation estimates. We focus on the ${\rm L}^2$-stability of the sampling operator by using notions from frame theory. This approach yields particularly simple and transparent reconstruction procedures. We then apply these methods to the discretization of discrete series representations and to Paley-Wiener spaces on stratified Lie groups.; Comment: 18 pages

## ‣ Density of the Set of Generators of Wavelet Systems

Cabrelli, Carlos; Molter, Ursula
Tipo: Artigo de Revista Científica
Português
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Given a function $\psi$ in $\LL^2(\R^d)$, the affine (wavelet) system generated by $\psi$, associated to an invertible matrix $a$ and a lattice $\zG$, is the collection of functions $\{|\det a|^{j/2} \psi(a^jx-\gamma): j \in \Z, \gamma \in \zG\}$. In this article we prove that the set of functions generating affine systems that are a Riesz basis of $\LL^2(\R^d)$ is dense in $\LL^2(\R^d)$. We also prove that a stronger result is true for affine systems that are a frame of $\LL^2(\R^d)$. In this case we show that the generators associated to a fixed but arbitrary dilation are a dense set. Furthermore, we analyze the orthogonal case in which we prove that the set of generators of orthogonal (not necessarily complete) affine systems, that are compactly supported in frequency, are dense in the unit sphere of $\LL^2(\R^d)$ with the induced metric. As a byproduct we introduce the $p$-Grammian of a function and prove a convergence result of this Grammian as a function of the lattice. This result gives insight in the problem of oversampling of affine systems.; Comment: 15 pages-to appear in Constructive Approximation. Revised version

## ‣ Use of operator algebras in the analysis of measures from wavelets and iterated function systems

Jorgensen, Palle E. T.
Tipo: Artigo de Revista Científica
Publicado em 15/09/2005 Português
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In this paper, we show how a class of operators used in the analysis of measures from wavelets and iterated function systems may be understood from a special family of representations of Cuntz algebras.

## ‣ Groups, Wavelets, and Wavelet Sets

Olafsson, Gestur; Speegle, Darrin
Tipo: Artigo de Revista Científica
Publicado em 23/07/2003 Português
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Wavelet and frames have become a widely used tool in mathematics, physics, and applied science during the last decade. This article gives an overview over some well known results about the continuous and discrete wavelet transforms and groups acting on $\mathbb{R}^n$. We also show how this action can give rise to wavelets, and in particular, MSF wavelets)in $L^2(\mathbb{R}^n)$.

## ‣ Multiresolution in the Bergman space

Pap, Margit
Tipo: Artigo de Revista Científica
Português
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In this paper we give a multiresolution construction in Bergman space. The successful application of rational orthogonal bases needs a priori knowledge of the poles of the transfer function that may cause a drawback of the method. We give a set of poles and using them we will generate a multiresolution in $A^2$. We study the upper and lower density of this set, and we give sufficient conditions for this set to be interpolating or sampling sequence for the Bergman space. The construction is an analogy with the discrete affine wavelets, and in fact is the discretization of the continuous voice transform generated by a representation of the Blaschke group over the Bergman space. The constructed discretization scheme gives opportunity of practical realization of hyperbolic wavelet representation of signals belonging to the Bergman space if we can measure their values on a given set of points inside the unit disc. Convergence properties of the hyperbolic wavelet representation will be studied.; Comment: 15 pages, revised version

## ‣ Adaptive Nonparametric Regression on Spin Fiber Bundles

Durastanti, Claudio; Geller, Daryl; Marinucci, Domenico