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COMPUTER SCIENCE (1153 journals)                  1 2 3 4 5 6 | Last

Showing 1 - 200 of 872 Journals sorted alphabetically
3D Printing and Additive Manufacturing     Full-text available via subscription   (Followers: 12)
Abakós     Open Access   (Followers: 3)
Academy of Information and Management Sciences Journal     Full-text available via subscription   (Followers: 67)
ACM Computing Surveys     Hybrid Journal   (Followers: 23)
ACM Journal on Computing and Cultural Heritage     Hybrid Journal   (Followers: 8)
ACM Journal on Emerging Technologies in Computing Systems     Hybrid Journal   (Followers: 13)
ACM Transactions on Accessible Computing (TACCESS)     Hybrid Journal   (Followers: 4)
ACM Transactions on Algorithms (TALG)     Hybrid Journal   (Followers: 16)
ACM Transactions on Applied Perception (TAP)     Hybrid Journal   (Followers: 6)
ACM Transactions on Architecture and Code Optimization (TACO)     Hybrid Journal   (Followers: 9)
ACM Transactions on Autonomous and Adaptive Systems (TAAS)     Hybrid Journal   (Followers: 7)
ACM Transactions on Computation Theory (TOCT)     Hybrid Journal   (Followers: 11)
ACM Transactions on Computational Logic (TOCL)     Hybrid Journal   (Followers: 4)
ACM Transactions on Computer Systems (TOCS)     Hybrid Journal   (Followers: 18)
ACM Transactions on Computer-Human Interaction     Hybrid Journal   (Followers: 12)
ACM Transactions on Computing Education (TOCE)     Hybrid Journal   (Followers: 3)
ACM Transactions on Design Automation of Electronic Systems (TODAES)     Hybrid Journal   (Followers: 1)
ACM Transactions on Economics and Computation     Hybrid Journal  
ACM Transactions on Embedded Computing Systems (TECS)     Hybrid Journal   (Followers: 4)
ACM Transactions on Information Systems (TOIS)     Hybrid Journal   (Followers: 20)
ACM Transactions on Intelligent Systems and Technology (TIST)     Hybrid Journal   (Followers: 9)
ACM Transactions on Interactive Intelligent Systems (TiiS)     Hybrid Journal   (Followers: 4)
ACM Transactions on Multimedia Computing, Communications, and Applications (TOMCCAP)     Hybrid Journal   (Followers: 10)
ACM Transactions on Reconfigurable Technology and Systems (TRETS)     Hybrid Journal   (Followers: 7)
ACM Transactions on Sensor Networks (TOSN)     Hybrid Journal   (Followers: 8)
ACM Transactions on Speech and Language Processing (TSLP)     Hybrid Journal   (Followers: 11)
ACM Transactions on Storage     Hybrid Journal  
ACS Applied Materials & Interfaces     Full-text available via subscription   (Followers: 21)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 3)
Acta Universitatis Cibiniensis. Technical Series     Open Access  
Ad Hoc Networks     Hybrid Journal   (Followers: 11)
Adaptive Behavior     Hybrid Journal   (Followers: 11)
Advanced Engineering Materials     Hybrid Journal   (Followers: 26)
Advanced Science Letters     Full-text available via subscription   (Followers: 7)
Advances in Adaptive Data Analysis     Hybrid Journal   (Followers: 8)
Advances in Artificial Intelligence     Open Access   (Followers: 15)
Advances in Artificial Neural Systems     Open Access   (Followers: 4)
Advances in Calculus of Variations     Hybrid Journal   (Followers: 2)
Advances in Catalysis     Full-text available via subscription   (Followers: 5)
Advances in Computational Mathematics     Hybrid Journal   (Followers: 15)
Advances in Computer Science : an International Journal     Open Access   (Followers: 13)
Advances in Computing     Open Access   (Followers: 3)
Advances in Data Analysis and Classification     Hybrid Journal   (Followers: 53)
Advances in Engineering Software     Hybrid Journal   (Followers: 25)
Advances in Geosciences (ADGEO)     Open Access   (Followers: 10)
Advances in Human Factors/Ergonomics     Full-text available via subscription   (Followers: 25)
Advances in Human-Computer Interaction     Open Access   (Followers: 19)
Advances in Materials Sciences     Open Access   (Followers: 16)
Advances in Operations Research     Open Access   (Followers: 11)
Advances in Parallel Computing     Full-text available via subscription   (Followers: 7)
Advances in Porous Media     Full-text available via subscription   (Followers: 4)
Advances in Remote Sensing     Open Access   (Followers: 37)
Advances in Science and Research (ASR)     Open Access   (Followers: 6)
Advances in Technology Innovation     Open Access  
AEU - International Journal of Electronics and Communications     Hybrid Journal   (Followers: 8)
African Journal of Information and Communication     Open Access   (Followers: 6)
African Journal of Mathematics and Computer Science Research     Open Access   (Followers: 4)
Air, Soil & Water Research     Open Access   (Followers: 7)
AIS Transactions on Human-Computer Interaction     Open Access   (Followers: 6)
Algebras and Representation Theory     Hybrid Journal   (Followers: 1)
Algorithms     Open Access   (Followers: 10)
American Journal of Computational and Applied Mathematics     Open Access   (Followers: 3)
American Journal of Computational Mathematics     Open Access   (Followers: 4)
American Journal of Information Systems     Open Access   (Followers: 6)
American Journal of Sensor Technology     Open Access   (Followers: 2)
Anais da Academia Brasileira de Ciências     Open Access   (Followers: 2)
Analog Integrated Circuits and Signal Processing     Hybrid Journal   (Followers: 5)
Analysis in Theory and Applications     Hybrid Journal  
Animation Practice, Process & Production     Hybrid Journal   (Followers: 5)
Annals of Combinatorics     Hybrid Journal   (Followers: 3)
Annals of Data Science     Hybrid Journal   (Followers: 8)
Annals of Mathematics and Artificial Intelligence     Hybrid Journal   (Followers: 6)
Annals of Pure and Applied Logic     Open Access   (Followers: 2)
Annals of Software Engineering     Hybrid Journal   (Followers: 12)
Annual Reviews in Control     Hybrid Journal   (Followers: 6)
Anuario Americanista Europeo     Open Access  
Applicable Algebra in Engineering, Communication and Computing     Hybrid Journal   (Followers: 2)
Applied and Computational Harmonic Analysis     Full-text available via subscription   (Followers: 2)
Applied Artificial Intelligence: An International Journal     Hybrid Journal   (Followers: 14)
Applied Categorical Structures     Hybrid Journal   (Followers: 2)
Applied Clinical Informatics     Hybrid Journal   (Followers: 1)
Applied Computational Intelligence and Soft Computing     Open Access   (Followers: 12)
Applied Computer Systems     Open Access   (Followers: 1)
Applied Informatics     Open Access  
Applied Mathematics and Computation     Hybrid Journal   (Followers: 32)
Applied Medical Informatics     Open Access   (Followers: 10)
Applied Numerical Mathematics     Hybrid Journal   (Followers: 5)
Applied Soft Computing     Hybrid Journal   (Followers: 16)
Applied Spatial Analysis and Policy     Hybrid Journal   (Followers: 4)
Architectural Theory Review     Hybrid Journal   (Followers: 3)
Archive of Applied Mechanics     Hybrid Journal   (Followers: 4)
Archive of Numerical Software     Open Access  
Archives and Museum Informatics     Hybrid Journal   (Followers: 122)
Archives of Computational Methods in Engineering     Hybrid Journal   (Followers: 4)
Artifact     Hybrid Journal   (Followers: 2)
Artificial Life     Hybrid Journal   (Followers: 5)
Asia Pacific Journal on Computational Engineering     Open Access  
Asia-Pacific Journal of Information Technology and Multimedia     Open Access   (Followers: 1)
Asian Journal of Computer Science and Information Technology     Open Access  
Asian Journal of Control     Hybrid Journal  
Assembly Automation     Hybrid Journal   (Followers: 2)
at - Automatisierungstechnik     Hybrid Journal   (Followers: 1)
Australian Educational Computing     Open Access  
Automatic Control and Computer Sciences     Hybrid Journal   (Followers: 3)
Automatic Documentation and Mathematical Linguistics     Hybrid Journal   (Followers: 5)
Automatica     Hybrid Journal   (Followers: 9)
Automation in Construction     Hybrid Journal   (Followers: 6)
Autonomous Mental Development, IEEE Transactions on     Hybrid Journal   (Followers: 8)
Basin Research     Hybrid Journal   (Followers: 4)
Behaviour & Information Technology     Hybrid Journal   (Followers: 52)
Bioinformatics     Hybrid Journal   (Followers: 293)
Biomedical Engineering     Hybrid Journal   (Followers: 16)
Biomedical Engineering and Computational Biology     Open Access   (Followers: 13)
Biomedical Engineering, IEEE Reviews in     Full-text available via subscription   (Followers: 17)
Biomedical Engineering, IEEE Transactions on     Hybrid Journal   (Followers: 32)
Briefings in Bioinformatics     Hybrid Journal   (Followers: 45)
British Journal of Educational Technology     Hybrid Journal   (Followers: 119)
Broadcasting, IEEE Transactions on     Hybrid Journal   (Followers: 10)
c't Magazin fuer Computertechnik     Full-text available via subscription   (Followers: 2)
CALCOLO     Hybrid Journal  
Calphad     Hybrid Journal  
Canadian Journal of Electrical and Computer Engineering     Full-text available via subscription   (Followers: 13)
Catalysis in Industry     Hybrid Journal   (Followers: 1)
CEAS Space Journal     Hybrid Journal  
Cell Communication and Signaling     Open Access   (Followers: 1)
Central European Journal of Computer Science     Hybrid Journal   (Followers: 5)
CERN IdeaSquare Journal of Experimental Innovation     Open Access  
Chaos, Solitons & Fractals     Hybrid Journal   (Followers: 3)
Chemometrics and Intelligent Laboratory Systems     Hybrid Journal   (Followers: 15)
ChemSusChem     Hybrid Journal   (Followers: 7)
China Communications     Full-text available via subscription   (Followers: 7)
Chinese Journal of Catalysis     Full-text available via subscription   (Followers: 2)
CIN Computers Informatics Nursing     Full-text available via subscription   (Followers: 12)
Circuits and Systems     Open Access   (Followers: 16)
Clean Air Journal     Full-text available via subscription   (Followers: 2)
CLEI Electronic Journal     Open Access  
Clin-Alert     Hybrid Journal   (Followers: 1)
Cluster Computing     Hybrid Journal   (Followers: 1)
Cognitive Computation     Hybrid Journal   (Followers: 4)
COMBINATORICA     Hybrid Journal  
Combustion Theory and Modelling     Hybrid Journal   (Followers: 13)
Communication Methods and Measures     Hybrid Journal   (Followers: 11)
Communication Theory     Hybrid Journal   (Followers: 19)
Communications Engineer     Hybrid Journal   (Followers: 1)
Communications in Algebra     Hybrid Journal   (Followers: 3)
Communications in Partial Differential Equations     Hybrid Journal   (Followers: 3)
Communications of the ACM     Full-text available via subscription   (Followers: 53)
Communications of the Association for Information Systems     Open Access   (Followers: 18)
COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering     Hybrid Journal   (Followers: 3)
Complex & Intelligent Systems     Open Access  
Complex Adaptive Systems Modeling     Open Access  
Complex Analysis and Operator Theory     Hybrid Journal   (Followers: 2)
Complexity     Hybrid Journal   (Followers: 6)
Complexus     Full-text available via subscription  
Composite Materials Series     Full-text available via subscription   (Followers: 9)
Computación y Sistemas     Open Access  
Computation     Open Access  
Computational and Applied Mathematics     Hybrid Journal   (Followers: 2)
Computational and Mathematical Methods in Medicine     Open Access   (Followers: 2)
Computational and Mathematical Organization Theory     Hybrid Journal   (Followers: 2)
Computational and Structural Biotechnology Journal     Open Access   (Followers: 2)
Computational and Theoretical Chemistry     Hybrid Journal   (Followers: 9)
Computational Astrophysics and Cosmology     Open Access   (Followers: 1)
Computational Biology and Chemistry     Hybrid Journal   (Followers: 12)
Computational Chemistry     Open Access   (Followers: 2)
Computational Cognitive Science     Open Access   (Followers: 1)
Computational Complexity     Hybrid Journal   (Followers: 4)
Computational Condensed Matter     Open Access  
Computational Ecology and Software     Open Access   (Followers: 8)
Computational Economics     Hybrid Journal   (Followers: 9)
Computational Geosciences     Hybrid Journal   (Followers: 13)
Computational Linguistics     Open Access   (Followers: 23)
Computational Management Science     Hybrid Journal  
Computational Mathematics and Modeling     Hybrid Journal   (Followers: 8)
Computational Mechanics     Hybrid Journal   (Followers: 4)
Computational Methods and Function Theory     Hybrid Journal  
Computational Molecular Bioscience     Open Access   (Followers: 2)
Computational Optimization and Applications     Hybrid Journal   (Followers: 7)
Computational Particle Mechanics     Hybrid Journal   (Followers: 1)
Computational Research     Open Access   (Followers: 1)
Computational Science and Discovery     Full-text available via subscription   (Followers: 2)
Computational Science and Techniques     Open Access  
Computational Statistics     Hybrid Journal   (Followers: 13)
Computational Statistics & Data Analysis     Hybrid Journal   (Followers: 28)
Computer     Full-text available via subscription   (Followers: 83)
Computer Aided Surgery     Hybrid Journal   (Followers: 3)
Computer Applications in Engineering Education     Hybrid Journal   (Followers: 6)
Computer Communications     Hybrid Journal   (Followers: 10)
Computer Engineering and Applications Journal     Open Access   (Followers: 5)
Computer Journal     Hybrid Journal   (Followers: 7)
Computer Methods in Applied Mechanics and Engineering     Hybrid Journal   (Followers: 22)
Computer Methods in Biomechanics and Biomedical Engineering     Hybrid Journal   (Followers: 10)
Computer Methods in the Geosciences     Full-text available via subscription   (Followers: 1)
Computer Music Journal     Hybrid Journal   (Followers: 14)
Computer Physics Communications     Hybrid Journal   (Followers: 6)
Computer Science - Research and Development     Hybrid Journal   (Followers: 7)
Computer Science and Engineering     Open Access   (Followers: 17)
Computer Science and Information Technology     Open Access   (Followers: 11)
Computer Science Education     Hybrid Journal   (Followers: 12)
Computer Science Journal     Open Access   (Followers: 20)

        1 2 3 4 5 6 | Last

Journal Cover Applied and Computational Harmonic Analysis
  [SJR: 1.589]   [H-I: 65]   [2 followers]  Follow
   Full-text available via subscription Subscription journal
   ISSN (Print) 1063-5203 - ISSN (Online) 1096-603X
   Published by Elsevier Homepage  [3042 journals]
  • Decomposition matrices for the special case of data on the triangular
           lattice of SU(3)
    • Authors: M. Bodner; J. Patera; M. Szajewska
      Abstract: Publication date: September 2017
      Source:Applied and Computational Harmonic Analysis, Volume 43, Issue 2
      Author(s): M. Bodner, J. Patera, M. Szajewska
      A method for the decomposition of data functions sampled on a finite fragment of triangular lattices is described for the lattice corresponding to the simple Lie group S U ( 3 ) . The basic tile (fundamental region) of S U ( 3 ) is an equilateral triangle. The decomposition matrices refer to lattices that carry data of any density. This main result is summarized in Section 4 Theorem 2.

      PubDate: 2017-07-12T06:45:03Z
      DOI: 10.1016/j.acha.2017.02.003
  • Evaluation of small elements of the eigenvectors of certain symmetric
           tridiagonal matrices with high relative accuracy
    • Authors: Andrei Osipov
      Pages: 173 - 211
      Abstract: Publication date: September 2017
      Source:Applied and Computational Harmonic Analysis, Volume 43, Issue 2
      Author(s): Andrei Osipov
      Evaluation of the eigenvectors of symmetric tridiagonal matrices is one of the most basic tasks in numerical linear algebra. It is a widely known fact that, in the case of well separated eigenvalues, the eigenvectors can be evaluated with high relative accuracy. Nevertheless, in general, each coordinate of the eigenvector is evaluated with only high absolute accuracy. In particular, those coordinates whose magnitude is below the machine precision are not expected to be evaluated with any accuracy whatsoever. It turns out that, under certain conditions, frequently encountered in applications, small (e.g. 10 − 50 ) coordinates of eigenvectors of symmetric tridiagonal matrices can be evaluated with high relative accuracy. In this paper, we investigate such conditions, carry out the analysis, and describe the resulting numerical schemes. While our schemes can be viewed as a modification of already existing (and well known) numerical algorithms, the related error analysis appears to be new. Our results are illustrated via several numerical examples.

      PubDate: 2017-07-12T06:45:03Z
      DOI: 10.1016/j.acha.2015.12.002
  • Error bounds for compressed sensing algorithms with group sparsity: A
           unified approach
    • Authors: M. Eren Ahsen; M. Vidyasagar
      Pages: 212 - 232
      Abstract: Publication date: September 2017
      Source:Applied and Computational Harmonic Analysis, Volume 43, Issue 2
      Author(s): M. Eren Ahsen, M. Vidyasagar
      In compressed sensing, in order to recover a sparse or nearly sparse vector from possibly noisy measurements, the most popular approach is ℓ 1 -norm minimization. Upper bounds for the ℓ 2 -norm of the error between the true and estimated vectors are given in [1] and reviewed in [2], while bounds for the ℓ 1 -norm are given in [3]. When the unknown vector is not conventionally sparse but is “group sparse” instead, a variety of alternatives to the ℓ 1 -norm have been proposed in the literature, including the group LASSO, sparse group LASSO, and group LASSO with tree structured overlapping groups. However, no error bounds are available for any of these modified objective functions. In the present paper, a unified approach is presented for deriving upper bounds on the error between the true vector and its approximation, based on the notion of decomposable and γ-decomposable norms. The bounds presented cover all of the norms mentioned above, and also provide a guideline for choosing norms in future to accommodate alternate forms of sparsity.

      PubDate: 2017-07-12T06:45:03Z
      DOI: 10.1016/j.acha.2015.11.006
  • Neural network with unbounded activation functions is universal
    • Authors: Sho Sonoda; Noboru Murata
      Pages: 233 - 268
      Abstract: Publication date: September 2017
      Source:Applied and Computational Harmonic Analysis, Volume 43, Issue 2
      Author(s): Sho Sonoda, Noboru Murata
      This paper presents an investigation of the approximation property of neural networks with unbounded activation functions, such as the rectified linear unit (ReLU), which is the new de-facto standard of deep learning. The ReLU network can be analyzed by the ridgelet transform with respect to Lizorkin distributions. By showing three reconstruction formulas by using the Fourier slice theorem, the Radon transform, and Parseval's relation, it is shown that a neural network with unbounded activation functions still satisfies the universal approximation property. As an additional consequence, the ridgelet transform, or the backprojection filter in the Radon domain, is what the network learns after backpropagation. Subject to a constructive admissibility condition, the trained network can be obtained by simply discretizing the ridgelet transform, without backpropagation. Numerical examples not only support the consistency of the admissibility condition but also imply that some non-admissible cases result in low-pass filtering.

      PubDate: 2017-07-12T06:45:03Z
      DOI: 10.1016/j.acha.2015.12.005
  • A multifractal formalism for non-concave and non-increasing spectra: The
           leaders profile method
    • Authors: Céline Esser; Thomas Kleyntssens; Samuel Nicolay
      Pages: 269 - 291
      Abstract: Publication date: September 2017
      Source:Applied and Computational Harmonic Analysis, Volume 43, Issue 2
      Author(s): Céline Esser, Thomas Kleyntssens, Samuel Nicolay
      We present an implementation of a multifractal formalism based on the types of histogram of wavelet leaders. This method yields non-concave spectra and is not limited to their increasing part. We show both from the theoretical and from the applied points of view that this approach is more efficient than the wavelet-based multifractal formalisms previously introduced.

      PubDate: 2017-07-12T06:45:03Z
      DOI: 10.1016/j.acha.2015.12.006
  • Fully discrete needlet approximation on the sphere
    • Authors: Yu Guang Wang; Quoc T. Le Gia; Ian H. Sloan; Robert S. Womersley
      Pages: 292 - 316
      Abstract: Publication date: September 2017
      Source:Applied and Computational Harmonic Analysis, Volume 43, Issue 2
      Author(s): Yu Guang Wang, Quoc T. Le Gia, Ian H. Sloan, Robert S. Womersley
      Spherical needlets are highly localized radial polynomials on the sphere S d ⊂ R d + 1 , d ≥ 2 , with centers at the nodes of a suitable cubature rule. The original semidiscrete spherical needlet approximation of Narcowich, Petrushev and Ward is not computable, in that the needlet coefficients depend on inner product integrals. In this work we approximate these integrals by a second quadrature rule with an appropriate degree of precision, to construct a fully discrete needlet approximation. We prove that the resulting approximation is equivalent to filtered hyperinterpolation, that is to a filtered Fourier–Laplace series partial sum with inner products replaced by appropriate cubature sums. It follows that the L p -error of discrete needlet approximation of order J for 1 ≤ p ≤ ∞ and s > d / p has for a function f in the Sobolev space W p s ( S d ) the optimal rate of convergence in the sense of optimal recovery, namely O ( 2 − J s ) . Moreover, this is achieved with a filter function that is of smoothness class C ⌊ d + 3 2 ⌋ , in contrast to the usually assumed C ∞ . A numerical experiment for a class of functions in known Sobolev smoothness classes gives L 2 errors for the fully discrete needlet approximation that are almost identical to those for the original semidiscrete needlet approximation. Another experiment uses needlets over the whole sphere for the lower levels together with high-level needlets with centers restricted to a local region. The resulting errors are reduced in the local region away from the boundary, indicating that local refinement in special regions is a promising strategy.

      PubDate: 2017-07-12T06:45:03Z
      DOI: 10.1016/j.acha.2016.01.003
  • Appell sequences, continuous wavelet transforms and series expansions
    • Authors: Say Song Goh; Tim N.T. Goodman; S.L. Lee
      Pages: 317 - 345
      Abstract: Publication date: September 2017
      Source:Applied and Computational Harmonic Analysis, Volume 43, Issue 2
      Author(s): Say Song Goh, Tim N.T. Goodman, S.L. Lee
      A series expansion with remainder for functions in a Sobolev space is derived in terms of the classical Bernoulli polynomials, the B-spline scale-space and the continuous wavelet transforms with the derivatives of the standardized B-splines as mother wavelets. In the limit as their orders tend to infinity, the B-splines and their derivatives converge to the Gaussian function and its derivatives respectively, the associated Bernoulli polynomials converge to the Hermite polynomials, and the corresponding series expansion is an expansion in terms of the Hermite polynomials, the Gaussian scale-space and the continuous wavelet transforms with the derivatives of the Gaussian function as mother wavelets. A similar expansion is also derived in terms of continuous wavelet transforms in which the mother wavelets are the spline framelets that approximate the derivatives of the standardized B-splines.

      PubDate: 2017-07-12T06:45:03Z
      DOI: 10.1016/j.acha.2016.01.005
  • Explicit universal sampling sets in finite vector spaces
    • Authors: Lucia Morotti
      Pages: 354 - 369
      Abstract: Publication date: September 2017
      Source:Applied and Computational Harmonic Analysis, Volume 43, Issue 2
      Author(s): Lucia Morotti
      In this paper we construct explicit sampling sets and present reconstruction algorithms for Fourier signals on finite vector spaces G, with G = p r for a suitable prime p. The two sampling sets have sizes of order O ( p t 2 r 2 ) and O ( p t 2 r 3 log ⁡ ( p ) ) respectively, where t is the number of large coefficients in the Fourier transform. The algorithms approximate the function up to a small constant of the best possible approximation with t non-zero Fourier coefficients. The fastest of the algorithms has complexity O ( p 2 t 2 r 3 log ⁡ ( p ) ) .

      PubDate: 2017-07-12T06:45:03Z
      DOI: 10.1016/j.acha.2016.06.001
  • A note on Markov normalized magnetic eigenmaps
    • Authors: Alexander Cloninger
      Pages: 370 - 380
      Abstract: Publication date: September 2017
      Source:Applied and Computational Harmonic Analysis, Volume 43, Issue 2
      Author(s): Alexander Cloninger
      We note that building a magnetic Laplacian from the Markov transition matrix, rather than the graph adjacency matrix, yields several benefits for the magnetic eigenmaps algorithm. The two largest benefits are that the embedding becomes more stable as a function of the rotation parameter g, and the principal eigenvector of the magnetic Laplacian now converges to the page rank of the network as a function of diffusion time. We show empirically that this normalization improves the phase and real/imaginary embeddings of the low-frequency eigenvectors of the magnetic Laplacian.

      PubDate: 2017-07-12T06:45:03Z
      DOI: 10.1016/j.acha.2016.11.002
  • Recovery analysis for weighted ℓ1-minimization using the null space
    • Authors: Hassan Mansour; Rayan Saab
      Pages: 23 - 38
      Abstract: Publication date: July 2017
      Source:Applied and Computational Harmonic Analysis, Volume 43, Issue 1
      Author(s): Hassan Mansour, Rayan Saab
      We study the recovery of sparse signals from underdetermined linear measurements when a potentially erroneous support estimate is available. Our results are twofold. First, we derive necessary and sufficient conditions for signal recovery from compressively sampled measurements using weighted ℓ 1 -norm minimization. These conditions, which depend on the choice of weights as well as the size and accuracy of the support estimate, are on the null space of the measurement matrix. They can guarantee recovery even when standard ℓ 1 minimization fails. Second, we derive bounds on the number of Gaussian measurements for these conditions to be satisfied, i.e., for weighted ℓ 1 minimization to successfully recover all sparse signals whose support has been estimated sufficiently accurately. Our bounds show that weighted ℓ 1 minimization requires significantly fewer measurements than standard ℓ 1 minimization when the support estimate is relatively accurate.

      PubDate: 2017-05-17T15:00:34Z
      DOI: 10.1016/j.acha.2015.10.005
  • Far-field compression for fast kernel summation methods in high dimensions
    • Authors: William B. March; George Biros
      Pages: 39 - 75
      Abstract: Publication date: July 2017
      Source:Applied and Computational Harmonic Analysis, Volume 43, Issue 1
      Author(s): William B. March, George Biros
      We consider fast kernel summations in high dimensions: given a large set of points in d dimensions (with d ≫ 3 ) and a pair-potential function (the kernel function), we compute a weighted sum of all pairwise kernel interactions for each point in the set. Direct summation is equivalent to a (dense) matrix–vector multiplication and scales quadratically with the number of points. Fast kernel summation algorithms reduce this cost to log-linear or linear complexity. Treecodes and Fast Multipole Methods (FMMs) deliver tremendous speedups by constructing approximate representations of interactions of points that are far from each other. In algebraic terms, these representations correspond to low-rank approximations of blocks of the overall interaction matrix. Existing approaches require an excessive number of kernel evaluations with increasing d and number of points in the dataset. To address this issue, we use a randomized algebraic approach in which we first sample the rows of a block and then construct its approximate, low-rank interpolative decomposition. We examine the feasibility of this approach theoretically and experimentally. We provide a new theoretical result showing a tighter bound on the reconstruction error from uniformly sampling rows than the existing state-of-the-art. We demonstrate that our sampling approach is competitive with existing (but prohibitively expensive) methods from the literature. We also construct kernel matrices for the Laplacian, Gaussian, and polynomial kernels—all commonly used in physics and data analysis. We explore the numerical properties of blocks of these matrices, and show that they are amenable to our approach. Depending on the data set, our randomized algorithm can successfully compute low rank approximations in high dimensions. We report results for data sets with ambient dimensions from four to 1,000.

      PubDate: 2017-05-17T15:00:34Z
      DOI: 10.1016/j.acha.2015.09.007
  • A sampling theory for non-decaying signals
    • Authors: Ha Q. Nguyen; Michael Unser
      Pages: 76 - 93
      Abstract: Publication date: July 2017
      Source:Applied and Computational Harmonic Analysis, Volume 43, Issue 1
      Author(s): Ha Q. Nguyen, Michael Unser
      The classical assumption in sampling and spline theories is that the input signal is square-integrable, which prevents us from applying such techniques to signals that do not decay or even grow at infinity. In this paper, we develop a sampling theory for multidimensional non-decaying signals living in weighted L p spaces. The sampling and reconstruction of an analog signal can be done by a projection onto a shift-invariant subspace generated by an interpolating kernel. We show that, if this kernel and its biorthogonal counterpart are elements of appropriate hybrid-norm spaces, then both the sampling and the reconstruction are stable. This is an extension of earlier results by Aldroubi and Gröchenig. The extension is required because it allows us to develop the theory for the ideal sampling of non-decaying signals in weighted Sobolev spaces. When the d-dimensional signal and its d / p + ε derivatives, for arbitrarily small ε > 0 , grow no faster than a polynomial in the L p sense, the sampling operator is shown to be bounded even without a sampling kernel. As a consequence, the signal can also be interpolated from its samples with a nicely behaved interpolating kernel.

      PubDate: 2017-05-17T15:00:34Z
      DOI: 10.1016/j.acha.2015.10.006
  • Gabor frames of Gaussian beams for the Schrödinger equation
    • Authors: Michele Berra; Iulia Martina Bulai; Elena Cordero; Fabio Nicola
      Pages: 94 - 121
      Abstract: Publication date: July 2017
      Source:Applied and Computational Harmonic Analysis, Volume 43, Issue 1
      Author(s): Michele Berra, Iulia Martina Bulai, Elena Cordero, Fabio Nicola
      The present paper is devoted to the semiclassical analysis of linear Schrödinger equations from a Gabor frame perspective. We consider (time-dependent) smooth Hamiltonians with at most quadratic growth. Then we construct higher order parametrices for the corresponding Schrödinger equations by means of ħ-Gabor frames, as recently defined by M. de Gosson, and we provide precise L 2 -estimates of their accuracy, in terms of the Planck constant ħ. Nonlinear parametrices, in the spirit of the nonlinear approximation, are also presented. Numerical experiments are exhibited to compare our results with the early literature.

      PubDate: 2017-05-17T15:00:34Z
      DOI: 10.1016/j.acha.2015.11.001
  • High-dimensional change-point estimation: Combining filtering with convex
    • Authors: Yong Sheng Soh; Venkat Chandrasekaran
      Pages: 122 - 147
      Abstract: Publication date: July 2017
      Source:Applied and Computational Harmonic Analysis, Volume 43, Issue 1
      Author(s): Yong Sheng Soh, Venkat Chandrasekaran
      We consider change-point estimation in a sequence of high-dimensional signals given noisy observations. Classical approaches to this problem such as the filtered derivative method are useful for sequences of scalar-valued signals, but they have undesirable scaling behavior in the high-dimensional setting. However, many high-dimensional signals encountered in practice frequently possess latent low-dimensional structure. Motivated by this observation, we propose a technique for high-dimensional change-point estimation that combines the filtered derivative approach from previous work with convex optimization methods based on atomic norm regularization, which are useful for exploiting structure in high-dimensional data. Our algorithm is applicable in online settings as it operates on small portions of the sequence of observations at a time, and it is well-suited to the high-dimensional setting both in terms of computational scalability and of statistical efficiency. The main result of this paper shows that our method performs change-point estimation reliably as long as the product of the smallest-sized change (the Euclidean-norm-squared of the difference between signals at a change-point) and the smallest distance between change-points (number of time instances) is larger than a Gaussian width parameter that characterizes the low-dimensional complexity of the underlying signal sequence.

      PubDate: 2017-05-17T15:00:34Z
      DOI: 10.1016/j.acha.2015.11.003
  • Frames of directional wavelets on n-dimensional spheres
    • Authors: I. Iglewska-Nowak
      Pages: 148 - 161
      Abstract: Publication date: July 2017
      Source:Applied and Computational Harmonic Analysis, Volume 43, Issue 1
      Author(s): I. Iglewska-Nowak
      The major goal of the paper is to prove that discrete frames of (directional) wavelets derived from an approximate identity exist. Additionally, a kind of energy conservation property is shown to hold in the case when a wavelet family is not its own reconstruction family. Although an additional constraint on the spectrum of the wavelet family must be satisfied, it is shown that all the wavelets so far defined in the literature possess this property.

      PubDate: 2017-05-17T15:00:34Z
      DOI: 10.1016/j.acha.2016.01.004
  • Indefinite kernels in least squares support vector machines and principal
           component analysis
    • Authors: Xiaolin Huang; Andreas Maier; Joachim Hornegger; Johan A.K. Suykens
      Pages: 162 - 172
      Abstract: Publication date: July 2017
      Source:Applied and Computational Harmonic Analysis, Volume 43, Issue 1
      Author(s): Xiaolin Huang, Andreas Maier, Joachim Hornegger, Johan A.K. Suykens
      Because of several successful applications, indefinite kernels have attracted many research interests in recent years. This paper addresses indefinite learning in the framework of least squares support vector machines (LS-SVM). Unlike existing indefinite kernel learning methods, which usually involve non-convex problems, the indefinite LS-SVM is still easy to solve, but the kernel trick and primal-dual relationship for LS-SVM with a Mercer kernel is no longer valid. In this paper, we give a feature space interpretation for indefinite LS-SVM. In the same framework, kernel principal component analysis with an infinite kernel is discussed as well. In numerical experiments, LS-SVM with indefinite kernels for classification and kernel principal component analysis is evaluated. Its good performance together with the feature space interpretation given in this paper imply the potential use of indefinite LS-SVM in real applications.

      PubDate: 2017-05-17T15:00:34Z
      DOI: 10.1016/j.acha.2016.09.001
  • Approximations in Sobolev spaces by prolate spheroidal wave functions
    • Authors: Aline Bonami; Abderrazek Karoui
      Pages: 361 - 377
      Abstract: Publication date: May 2017
      Source:Applied and Computational Harmonic Analysis, Volume 42, Issue 3
      Author(s): Aline Bonami, Abderrazek Karoui
      Recently, there is a growing interest in the spectral approximation by the Prolate Spheroidal Wave Functions (PSWFs) ψ n , c , c > 0 . This is due to the promising new contributions of these functions in various classical as well as emerging applications from Signal Processing, Geophysics, Numerical Analysis, etc. The PSWFs form a basis with remarkable properties not only for the space of band-limited functions with bandwidth c, but also for the Sobolev space H s ( [ − 1 , 1 ] ) . The quality of the spectral approximation and the choice of the parameter c when approximating a function in H s ( [ − 1 , 1 ] ) by its truncated PSWFs series expansion, are the main issues. By considering a function f ∈ H s ( [ − 1 , 1 ] ) as the restriction to [ − 1 , 1 ] of an almost time-limited and band-limited function, we try to give satisfactory answers to these two issues. Also, we illustrate the different results of this work by some numerical examples.

      PubDate: 2017-03-13T00:25:52Z
      DOI: 10.1016/j.acha.2015.09.001
  • Dynamical sampling
    • Authors: A. Aldroubi; C. Cabrelli; U. Molter; S. Tang
      Pages: 378 - 401
      Abstract: Publication date: May 2017
      Source:Applied and Computational Harmonic Analysis, Volume 42, Issue 3
      Author(s): A. Aldroubi, C. Cabrelli, U. Molter, S. Tang
      Let Y = { f ( i ) , Af ( i ) , … , A l i f ( i ) : i ∈ Ω } , where A is a bounded operator on ℓ 2 ( I ) . The problem under consideration is to find necessary and sufficient conditions on A , Ω , { l i : i ∈ Ω } in order to recover any f ∈ ℓ 2 ( I ) from the measurements Y. This is the so-called dynamical sampling problem in which we seek to recover a function f by combining coarse samples of f and its futures states A l f . We completely solve this problem in finite dimensional spaces, and for a large class of self adjoint operators in infinite dimensional spaces. In the latter case, although Y can be complete, using the Müntz–Szász Theorem we show it can never be a basis. We can also show that, when Ω is finite, Y is not a frame except for some very special cases. The existence of these special cases is derived from Carleson's Theorem for interpolating sequences in the Hardy space H 2 ( D ) . Finally, using the recently proved Kadison–Singer/Feichtinger theorem we show that the set obtained by normalizing the vectors of Y can never be a frame when Ω is finite.

      PubDate: 2017-03-13T00:25:52Z
      DOI: 10.1016/j.acha.2015.08.014
  • An analysis of wavelet frame based scattered data reconstruction
    • Authors: Jianbin Yang; Dominik Stahl; Zuowei Shen
      Pages: 480 - 507
      Abstract: Publication date: May 2017
      Source:Applied and Computational Harmonic Analysis, Volume 42, Issue 3
      Author(s): Jianbin Yang, Dominik Stahl, Zuowei Shen
      In real world applications many signals contain singularities, like edges in images. Recent wavelet frame based approaches were successfully applied to reconstruct scattered data from such functions while preserving these features. In this paper we present a recent approach which determines the approximant from shift invariant subspaces by minimizing an ℓ 1 -regularized least squares problem which makes additional use of the wavelet frame transform in order to preserve sharp edges. We give a detailed analysis of this approach, i.e., how the approximation error behaves dependent on data density and noise level. Moreover, a link to wavelet frame based image restoration models is established and the convergence of these models is analyzed. In the end, we present some numerical examples, for instance how to apply this approach to handle coarse-grained models in molecular dynamics.

      PubDate: 2017-03-13T00:25:52Z
      DOI: 10.1016/j.acha.2015.09.008
  • Weighted frames of exponentials and stable recovery of multidimensional
           functions from nonuniform Fourier samples
    • Authors: Ben Adcock; Milana Gataric; Anders C. Hansen
      Pages: 508 - 535
      Abstract: Publication date: May 2017
      Source:Applied and Computational Harmonic Analysis, Volume 42, Issue 3
      Author(s): Ben Adcock, Milana Gataric, Anders C. Hansen
      In this paper, we consider the problem of recovering a compactly supported multivariate function from a collection of pointwise samples of its Fourier transform taken nonuniformly. We do this by using the concept of weighted Fourier frames. A seminal result of Beurling shows that sampling points give rise to a classical Fourier frame provided they are relatively separated and of sufficient density. However, this result does not allow for arbitrary clustering of sampling points, as is often the case in practice. Whilst keeping the density condition sharp and dimension independent, our first result removes the separation condition and shows that density alone suffices. However, this result does not lead to estimates for the frame bounds. A known result of Gröchenig provides explicit estimates, but only subject to a density condition that deteriorates linearly with dimension. In our second result we improve these bounds by reducing the dimension dependence. In particular, we provide explicit frame bounds which are dimensionless for functions having compact support contained in a sphere. Next, we demonstrate how our two main results give new insight into a reconstruction algorithm—based on the existing generalized sampling framework—that allows for stable and quasi-optimal reconstruction in any particular basis from a finite collection of samples. Finally, we construct sufficiently dense sampling schemes that are often used in practice—jittered, radial and spiral sampling schemes—and provide several examples illustrating the effectiveness of our approach when tested on these schemes.

      PubDate: 2017-03-13T00:25:52Z
      DOI: 10.1016/j.acha.2015.09.006
  • An inequality for a periodic uncertainty constant
    • Authors: Elena A. Lebedeva
      Pages: 536 - 549
      Abstract: Publication date: May 2017
      Source:Applied and Computational Harmonic Analysis, Volume 42, Issue 3
      Author(s): Elena A. Lebedeva
      An inequality refining the lower bound for a periodic (Breitenberger) uncertainty constant is proved for a wide class of functions. A connection of uncertainty constants for periodic and non-periodic functions is extended to this class. A particular minimization problem for a non-periodic (Heisenberg) uncertainty constant is studied.

      PubDate: 2017-03-13T00:25:52Z
      DOI: 10.1016/j.acha.2015.12.003
  • PhaseLift is robust to a constant fraction of arbitrary errors
    • Authors: Paul Hand
      Pages: 550 - 562
      Abstract: Publication date: May 2017
      Source:Applied and Computational Harmonic Analysis, Volume 42, Issue 3
      Author(s): Paul Hand
      Consider the task of recovering an unknown n-vector from phaseless linear measurements. This nonconvex problem may be convexified into a semidefinite rank-one matrix recovery problem, known as PhaseLift. Under a linear number of Gaussian measurements, PhaseLift recovers the unknown vector exactly with high probability. Under noisy measurements, the solution to a variant of PhaseLift has error proportional to the ℓ 1 norm of the noise. In the present paper, we study the robustness of this variant of PhaseLift to gross, arbitrary corruptions. We prove that PhaseLift can tolerate noise and a small, fixed fraction of gross errors, even in the highly underdetermined regime where there are only O ( n ) measurements. The lifted phase retrieval problem can be viewed as a rank-one robust Principal Component Analysis (PCA) problem under generic rank-one measurements. From this perspective, the proposed convex program is simpler than the semidefinite version of the sparse-plus-low-rank formulation standard in the robust PCA literature. Specifically, the rank penalization through a trace term is unnecessary, and the resulting optimization program has no parameters that need to be chosen.

      PubDate: 2017-03-13T00:25:52Z
      DOI: 10.1016/j.acha.2016.01.001
  • The fast Slepian transform
    • Authors: Santhosh Karnik; Zhihui Zhu; Michael B. Wakin; Justin Romberg; Mark A. Davenport
      Abstract: Publication date: Available online 19 July 2017
      Source:Applied and Computational Harmonic Analysis
      Author(s): Santhosh Karnik, Zhihui Zhu, Michael B. Wakin, Justin Romberg, Mark A. Davenport
      The discrete prolate spheroidal sequences (DPSS's) provide an efficient representation for discrete signals that are perfectly timelimited and nearly bandlimited. Due to the high computational complexity of projecting onto the DPSS basis – also known as the Slepian basis – this representation is often overlooked in favor of the fast Fourier transform (FFT). We show that there exist fast constructions for computing approximate projections onto the leading Slepian basis elements. The complexity of the resulting algorithms is comparable to the FFT, and scales favorably as the quality of the desired approximation is increased. In the process of bounding the complexity of these algorithms, we also establish new nonasymptotic results on the eigenvalue distribution of discrete time-frequency localization operators. We then demonstrate how these algorithms allow us to efficiently compute the solution to certain least-squares problems that arise in signal processing. We also provide simulations comparing these fast, approximate Slepian methods to exact Slepian methods as well as the traditional FFT based methods.

      PubDate: 2017-07-24T07:52:31Z
      DOI: 10.1016/j.acha.2017.07.005
  • Functional Reproducing Kernel Hilbert Spaces for Non-Point-Evaluation
           Functional Data
    • Authors: Rui Wang; Yuesheng Xu
      Abstract: Publication date: Available online 18 July 2017
      Source:Applied and Computational Harmonic Analysis
      Author(s): Rui Wang, Yuesheng Xu
      Motivated by the need of processing non-point-evaluation functional data, we introduce the notion of functional reproducing kernel Hilbert spaces (FRKHSs). This space admits a unique functional reproducing kernel which reproduces a family of continuous linear functionals on the space. The theory of FRKHSs and the associated functional reproducing kernels are established. A special class of FRKHSs, which we call the perfect FRKHSs, are studied, which reproduce the family of the standard point-evaluation functionals and at the same time another different family of continuous linear (non-point-evaluation) functionals. The perfect FRKHSs are characterized in terms of features, especially for those with respect to integral functionals. In particular, several specific examples of the perfect FRKHSs are presented. We apply the theory of FRKHSs to sampling and regularized learning, where non-point-evaluation functional data are used. Specifically, a general complete reconstruction formula from linear functional values is established in the framework of FRKHSs. The average sampling and the reconstruction of vector-valued functions are considered in specific FRKHSs. We also investigate in the FRKHS setting the regularized learning schemes, which learn a target element from non-point-evaluation functional data. The desired representer theorems of the learning problems are established to demonstrate the key roles played by the FRKHSs and the functional reproducing kernels in machine learning from non-point-evaluation functional data. We finally illustrate that the continuity of linear functionals, used to obtain the non-point-evaluation functional data, on an FRKHS is necessary for the stability of the numerical reconstruction algorithm using the data.

      PubDate: 2017-07-24T07:52:31Z
      DOI: 10.1016/j.acha.2017.07.003
  • The unitary extension principle on locally compact abelian groups
    • Authors: Ole Christensen; Say Song Goh
      Abstract: Publication date: Available online 18 July 2017
      Source:Applied and Computational Harmonic Analysis
      Author(s): Ole Christensen, Say Song Goh
      The unitary extension principle (UEP) by Ron and Shen yields conditions for the construction of a multi-generated tight wavelet frame for L 2 ( R s ) based on a given refinable function. In this paper we show that the UEP can be generalized to locally compact abelian groups. In the general setting, the resulting frames are generated by modulates of a collection of functions; via the Fourier transform this corresponds to a generalized shift-invariant system. Both the stationary and the nonstationary case are covered. We provide general constructions, based on B-splines on the group itself as well as on characteristic functions on the dual group. Finally, we consider a number of concrete groups and derive explicit constructions of the resulting frames.

      PubDate: 2017-07-24T07:52:31Z
      DOI: 10.1016/j.acha.2017.07.004
  • Toward the classification of biangular harmonic frames
    • Authors: Peter G. Casazza; Amineh Farzannia; John I. Haas; Tin T. Tran
      Abstract: Publication date: Available online 28 June 2017
      Source:Applied and Computational Harmonic Analysis
      Author(s): Peter G. Casazza, Amineh Farzannia, John I. Haas, Tin T. Tran
      Equiangular tight frames (ETFs) and biangular tight frames (BTFs) - sets of unit vectors with basis-like properties whose pairwise absolute inner products admit exactly one or two values, respectively - are useful for many applications. A well-understood class of ETFs are those which manifest as harmonic frames – vector sets defined in terms of the characters of finite abelian groups – because they are characterized by combinatorial objects called difference sets. This work is dedicated to the study of the underlying combinatorial structures of harmonic BTFs. We show that if a harmonic frame is generated by a divisible difference set, a partial difference set or by a special structure with certain Gauss summing properties – all three of which are generalizations of difference sets that fall under the umbrella term “bidifference set” – then it is either a BTF or an ETF. However, we also show that the relationship between harmonic BTFs and bidifference sets is not as straightforward as the correspondence between harmonic ETFs and difference sets, as there are examples of bidifference sets that do not generate harmonic BTFs. In addition, we study another class of combinatorial structures, the nested divisible difference sets, which yields an example of a harmonic BTF that is not generated by a bidifference set.

      PubDate: 2017-07-03T03:57:49Z
      DOI: 10.1016/j.acha.2017.06.004
  • A classification of continuous wavelet transforms in dimension three
    • Authors: Bradley Currey; Hartmut Führ; Vignon Oussa
      Abstract: Publication date: Available online 23 June 2017
      Source:Applied and Computational Harmonic Analysis
      Author(s): Bradley Currey, Hartmut Führ, Vignon Oussa
      This paper presents a full catalogue, up to conjugacy and subgroups of finite index, of all matrix groups H < GL ( 3 , R ) that give rise to a continuous wavelet transform with associated irreducible quasi-regular representation. For each group in this class, coorbit theory allows to consistently define spaces of sparse signals, and to construct atomic decompositions converging simultaneously in a whole range of these spaces. As an application of the classification, we investigate the existence of compactly supported admissible vectors and atoms for the groups.

      PubDate: 2017-07-03T03:57:49Z
      DOI: 10.1016/j.acha.2017.06.003
  • Distributed learning with multi-penalty regularization
    • Authors: Zheng-Chu Guo; Shao-Bo Lin; Lei Shi
      Abstract: Publication date: Available online 21 June 2017
      Source:Applied and Computational Harmonic Analysis
      Author(s): Zheng-Chu Guo, Shao-Bo Lin, Lei Shi
      In this paper, we study distributed learning with multi-penalty regularization based on a divide-and-conquer approach. Using Neumann expansion and a second order decomposition for difference of operator inverses approach, we derive optimal learning rates for distributed multi-penalty regularization in expectation. As a byproduct, we also deduce optimal learning rates for multi-penalty regularization, which was not given in the literature. These results are applied to the distributed manifold regularization and optimal learning rates are given.

      PubDate: 2017-06-21T17:19:46Z
      DOI: 10.1016/j.acha.2017.06.001
  • Bendlets: A second-order shearlet transform with bent elements
    • Authors: Christian Lessig; Philipp Petersen; Martin Schäfer
      Abstract: Publication date: Available online 16 June 2017
      Source:Applied and Computational Harmonic Analysis
      Author(s): Christian Lessig, Philipp Petersen, Martin Schäfer
      We introduce bendlets, a shearlet-like system that is based on anisotropic scaling, translation, shearing, and bending of a compactly supported generator. With shearing being linear and bending quadratic in spatial coordinates, bendlets provide what we term a second-order shearlet system. As we show in this article, the decay rates of the associated transform enable the precise characterization of location, orientation and curvature of discontinuities in piecewise constant images. These results yield an improvement over existing directional representation systems where curvature only controls the constant of the decay rate of the transform. We also detail the construction of shearlet systems of arbitrary order. A practical implementation of bendlets is provided as an extension of the ShearLab toolbox, which we use to verify our theoretical classification results.

      PubDate: 2017-06-21T17:19:46Z
      DOI: 10.1016/j.acha.2017.03.005
  • Compressed sensing with local structure: Uniform recovery guarantees for
           the sparsity in levels class
    • Authors: Chen Li; Ben Adcock
      Abstract: Publication date: Available online 6 June 2017
      Source:Applied and Computational Harmonic Analysis
      Author(s): Chen Li, Ben Adcock
      In compressed sensing, it is often desirable to consider signals possessing additional structure beyond sparsity. One such structured signal model – which forms the focus of this paper – is the local sparsity in levels class. This class has recently found applications in problems such as compressive imaging, multi-sensor acquisition systems and sparse regularization in inverse problems. In this paper we present uniform recovery guarantees for this class when the measurement matrix corresponds to a subsampled isometry. We do this by establishing a variant of the standard restricted isometry property for sparse in levels vectors, known as the restricted isometry property in levels. Interestingly, besides the usual log factors, our uniform recovery guarantees are simpler and less stringent than existing nonuniform recovery guarantees. For the particular case of discrete Fourier sampling with Haar wavelet sparsity, a corollary of our main theorem yields a new recovery guarantee which improves over the current state-of-the-art.

      PubDate: 2017-06-21T17:19:46Z
      DOI: 10.1016/j.acha.2017.05.006
  • Time-frequency analysis of bivariate signals
    • Authors: Julien Flamant; Nicolas Le Bihan; Pierre Chainais
      Abstract: Publication date: Available online 1 June 2017
      Source:Applied and Computational Harmonic Analysis
      Author(s): Julien Flamant, Nicolas Le Bihan, Pierre Chainais
      Many phenomena are described by bivariate signals or bidimensional vectors in applications ranging from radar to EEG, optics and oceanography. We show that an adequate quaternion Fourier transform permits to build relevant time-frequency representations of bivariate signals that naturally identify geometrical or polarization properties. First, a bivariate counterpart of the usual analytic signal of real signals is introduced, called the quaternion embedding of bivariate signals. Then two fundamental theorems ensure that a quaternion short term Fourier transform and a quaternion continuous wavelet transform are well defined and obey desirable properties such as conservation laws and reconstruction formulas. The resulting spectrograms and scalograms provide meaningful representations of both the time-frequency and geometrical/polarization content of the signal. Moreover the numerical implementation remains simply based on the use of FFT. A toolbox is available for reproducibility. Synthetic and real-world examples illustrate the relevance and efficiency of the proposed approach.

      PubDate: 2017-06-06T16:26:09Z
      DOI: 10.1016/j.acha.2017.05.007
  • Compressed sensing with structured sparsity and structured acquisition
    • Authors: Claire Boyer; Bigot Pierre Weiss
      Abstract: Publication date: Available online 26 May 2017
      Source:Applied and Computational Harmonic Analysis
      Author(s): Claire Boyer, Jérémie Bigot, Pierre Weiss
      Compressed Sensing (CS) is an appealing framework for applications such as Magnetic Resonance Imaging (MRI). However, up-to-date, the sensing schemes suggested by CS theories are made of random isolated measurements, which are usually incompatible with the physics of acquisition. To reflect the physical constraints of the imaging device, we introduce the notion of blocks of measurements: the sensing scheme is not a set of isolated measurements anymore, but a set of groups of measurements which may represent any arbitrary shape (parallel or radial lines for instance). Structured acquisition with blocks of measurements are easy to implement, and provide good reconstruction results in practice. However, very few results exist on the theoretical guarantees of CS reconstructions in this setting. In this paper, we derive new CS results for structured acquisitions and signals satisfying a prior structured sparsity. The obtained results provide a recovery probability of sparse vectors that explicitly depends on their support. Our results are thus support-dependent and offer the possibility for flexible assumptions on the sparsity structure. Moreover, the results are drawing-dependent, since we highlight an explicit dependency between the probability of reconstructing a sparse vector and the way of choosing the blocks of measurements. Numerical simulations show that the proposed theory is faithful to experimental observations.

      PubDate: 2017-05-27T15:43:17Z
  • Minimax optimal procedures for testing the structure of multidimensional
    • Authors: John Aston; Florent Autin; Gerda Claeskens; Jean-Marc Freyermuth; Christophe Pouet
      Abstract: Publication date: Available online 18 May 2017
      Source:Applied and Computational Harmonic Analysis
      Author(s): John Aston, Florent Autin, Gerda Claeskens, Jean-Marc Freyermuth, Christophe Pouet
      We present a novel method for detecting some structural characteristics of multidimensional functions. We consider the multidimensional Gaussian white noise model with an anisotropic estimand. Using the relation between the Sobol decomposition and the geometry of multidimensional wavelet basis we can build test statistics for any of the Sobol functional components. We assess the asymptotical minimax optimality of these test statistics and show that they are optimal in presence of anisotropy with respect to the newly determined minimax rates of separation. An appropriate combination of these test statistics allows to test some general structural characteristics such as the atomic dimension or the presence of some variables. Numerical experiments show the potential of our method for studying spatio-temporal processes.

      PubDate: 2017-05-22T15:20:14Z
      DOI: 10.1016/j.acha.2017.05.003
  • Time-frequency and time-scale analysis of deformed stationary processes,
           with application to non-stationary sound modeling
    • Authors: Omer
      Abstract: Publication date: July 2017
      Source:Applied and Computational Harmonic Analysis, Volume 43, Issue 1
      Author(s): H. Omer, B. Torrésani
      A class of random non-stationary signals termed timbre×dynamics is introduced and studied. These signals are obtained by non-linear transformations of stationary random Gaussian signals, in such a way that the transformation can be approximated by translations in an appropriate representation domain. In such situations, approximate maximum likelihood estimation techniques can be derived, which yield simultaneous estimation of the transformation and the power spectrum of the underlying stationary signal. This paper focuses on the case of modulation and time warping of stationary signals, and proposes and studies estimation algorithms (based on time-frequency and time-scale representations respectively) for these quantities of interest. The proposed approach is validated on numerical simulations on synthetic signals, and examples on real life car engine sounds.

      PubDate: 2017-05-17T15:00:34Z
  • Strichartz estimate of the solutions for the free fractional Schrödinger
           equation with spatial variable coefficient
    • Authors: Jian Zhai; Bowen Zheng
      Abstract: Publication date: Available online 15 May 2017
      Source:Applied and Computational Harmonic Analysis
      Author(s): Jian Zhai, Bowen Zheng
      This paper studies the Strichartz estimate of the solutions for the free fractional Schrödinger equation with spatial variable coefficient, which arises from the integrable model of the inhomogeneous spherically symmetric HFSS. It is different from the classical fractional Schrödinger equation in which the Strichartz estimates have been proved. We establish some harmonic analysis tools such as the equivalence of the Sobolev type spaces W ˙ σ , 2 and H ˙ σ and Hankel type Littlewood-Paley theory. By utilizing these ingredients, we prove the Strichartz estimate.

      PubDate: 2017-05-17T15:00:34Z
      DOI: 10.1016/j.acha.2017.05.002
  • On the solution of elliptic partial differential equations on regions with
           corners II: Detailed analysis
    • Authors: Kirill Serkh
      Abstract: Publication date: Available online 15 May 2017
      Source:Applied and Computational Harmonic Analysis
      Author(s): Kirill Serkh
      In this paper we investigate the solution of boundary value problems on polygonal domains for elliptic partial differential equations. Previously, we observed that when the boundary value problems are formulated as boundary integral equations of classical potential theory, the solutions are representable by series of elementary functions, to arbitrary order, for all but finitely many values of the angles. Here, we extend this observation to all values of the angles. We show that the solutions near corners are representable, to arbitrary order, by linear combinations of certain non-integer powers and non-integer powers multiplied by logarithms.

      PubDate: 2017-05-17T15:00:34Z
      DOI: 10.1016/j.acha.2017.05.001
  • Computing reconstructions from nonuniform Fourier samples: Universality of
           stability barriers and stable sampling rates
    • Authors: Ben Adcock; Milana Gataric; José Luis Romero
      Abstract: Publication date: Available online 12 May 2017
      Source:Applied and Computational Harmonic Analysis
      Author(s): Ben Adcock, Milana Gataric, José Luis Romero
      We study the problem of recovering an unknown compactly-supported multivariate function from samples of its Fourier transform that are acquired nonuniformly, i.e. not necessarily on a uniform Cartesian grid. Reconstruction problems of this kind arise in various imaging applications, where Fourier samples are taken along radial lines or spirals for example. Specifically, we consider finite-dimensional reconstructions, where a limited number of samples is available, and investigate the rate of convergence of such approximate solutions and their numerical stability. We show that the proportion of Fourier samples that allow for stable approximations of a given numerical accuracy is independent of the specific sampling geometry and is therefore universal for different sampling scenarios. This allows us to relate both sufficient and necessary conditions for different sampling setups and to exploit several results that were previously available only for very specific sampling geometries. The results are obtained by developing: (i) a transference argument for different measures of the concentration of the Fourier transform and Fourier samples; (ii) frame bounds valid up to the critical sampling density, which depend explicitly on the sampling set and the spectrum. As an application, we identify sufficient and necessary conditions for stable and accurate reconstruction of algebraic polynomials or wavelet coefficients from nonuniform Fourier data.

      PubDate: 2017-05-17T15:00:34Z
      DOI: 10.1016/j.acha.2017.05.004
  • Rotation invariant, Riesz bases of directional wavelets
    • Authors: Sylvain Durand
      Abstract: Publication date: Available online 20 April 2017
      Source:Applied and Computational Harmonic Analysis
      Author(s): Sylvain Durand
      This article addresses the issue of designing bases for L 2 ( R 2 ) that are generated by translations, rotations and dilations of a single mother wavelet ψ. We show how this construction can be simplified by setting an odd number of directions and by choosing properly the phase of the Fourier transform of ψ. A large part of the article is devoted to the proof of theorems that give sufficient conditions for ψ to generate a Riesz sequence and a Riesz basis for L 2 ( R 2 ) . An example of Riesz sequence whose restriction to each scale is orthonormal is set. Theoretical results are confirmed by numerical experiments where a discrete directional wavelet transform is introduced.

      PubDate: 2017-05-17T15:00:34Z
      DOI: 10.1016/j.acha.2017.04.001
  • Schatten properties, nuclearity and minimality of phase shift invariant
    • Authors: Joachim Toft
      Abstract: Publication date: Available online 20 April 2017
      Source:Applied and Computational Harmonic Analysis
      Author(s): Joachim Toft
      We extend Feichtinger's minimality property on the smallest non-trivial time-frequency shift invariant Banach space, to the quasi-Banach case. Analogous properties are deduced for certain matrix spaces. We use these results to prove that the pseudo-differential operator Op ( a ) is a Schatten-q operator from M ∞ to M p and r-nuclear operator from M ∞ to M r when a ∈ M r for suitable p, q and r in ( 0 , ∞ ] .

      PubDate: 2017-05-17T15:00:34Z
      DOI: 10.1016/j.acha.2017.04.003
  • Fast and provable algorithms for spectrally sparse signal reconstruction
           via low-rank Hankel matrix completion
    • Authors: Jian-Feng Cai; Tianming Wang; Ke Wei
      Abstract: Publication date: Available online 19 April 2017
      Source:Applied and Computational Harmonic Analysis
      Author(s): Jian-Feng Cai, Tianming Wang, Ke Wei
      A spectrally sparse signal of order r is a mixture of r damped or undamped complex sinusoids. This paper investigates the problem of reconstructing spectrally sparse signals from a random subset of n regular time domain samples, which can be reformulated as a low rank Hankel matrix completion problem. We introduce an iterative hard thresholding (IHT) algorithm and a fast iterative hard thresholding (FIHT) algorithm for efficient reconstruction of spectrally sparse signals via low rank Hankel matrix completion. Theoretical recovery guarantees have been established for FIHT, showing that O ( r 2 log 2 ⁡ ( n ) ) number of samples are sufficient for exact recovery with high probability. Empirical performance comparisons establish significant computational advantages for IHT and FIHT. In particular, numerical simulations on 3D arrays demonstrate the capability of FIHT on handling large and high-dimensional real data.

      PubDate: 2017-05-17T15:00:34Z
      DOI: 10.1016/j.acha.2017.04.004
  • Multidimensional butterfly factorization
    • Authors: Yingzhou Li; Haizhao Yang; Lexing Ying
      Abstract: Publication date: Available online 18 April 2017
      Source:Applied and Computational Harmonic Analysis
      Author(s): Yingzhou Li, Haizhao Yang, Lexing Ying
      This paper introduces the multidimensional butterfly factorization as a data-sparse representation of multidimensional kernel matrices that satisfy the complementary low-rank property. This factorization approximates such a kernel matrix of size N × N with a product of O ( log ⁡ N ) sparse matrices, each of which contains O ( N ) nonzero entries. We also propose efficient algorithms for constructing this factorization when either (i) a fast algorithm for applying the kernel matrix and its adjoint is available or (ii) every entry of the kernel matrix can be evaluated in O ( 1 ) operations. For the kernel matrices of multidimensional Fourier integral operators, for which the complementary low-rank property is not satisfied due to a singularity at the origin, we extend this factorization by combining it with either a polar coordinate transformation or a multiscale decomposition of the integration domain to overcome the singularity. Numerical results are provided to demonstrate the efficiency of the proposed algorithms.

      PubDate: 2017-05-17T15:00:34Z
      DOI: 10.1016/j.acha.2017.04.002
  • Stable separation and super-resolution of mixture models
    • Authors: Yuanxin Li; Yuejie Chi
      Abstract: Publication date: Available online 1 April 2017
      Source:Applied and Computational Harmonic Analysis
      Author(s): Yuanxin Li, Yuejie Chi
      We consider simultaneously identifying the membership and locations of point sources that are convolved with different band-limited point spread functions, from the observation of their superpositions. This problem arises in three-dimensional super-resolution single-molecule imaging, neural spike sorting, multi-user channel identification, among other applications. We propose a novel algorithm, based on convex programming, and establish its near-optimal performance guarantee for exact recovery in the noise-free setting by exploiting the spectral sparsity of the point source models as well as the incoherence between point spread functions. Furthermore, robustness of the recovery algorithm in the presence of bounded noise is also established. Numerical examples are provided to demonstrate the effectiveness of the proposed approach.

      PubDate: 2017-05-17T15:00:34Z
      DOI: 10.1016/j.acha.2017.03.003
  • Fixed-point algorithms for frequency estimation and structured low rank
    • Authors: Fredrik Andersson; Marcus Carlsson
      Abstract: Publication date: Available online 1 April 2017
      Source:Applied and Computational Harmonic Analysis
      Author(s): Fredrik Andersson, Marcus Carlsson
      We develop fixed-point algorithms for the approximation of structured matrices with rank penalties. In particular we use these fixed-point algorithms for making approximations by sums of exponentials, i.e., frequency estimation. For the basic formulation of the fixed-point algorithm we show that it converges to the solution of a related minimization problem, namely the one obtained by replacing the original objective function with its convex envelope and keeping the structured matrix constraint unchanged. It often happens that this solution agrees with the solution to the original minimization problem, and we provide a simple criterion for when this is true. We also provide more general fixed-point algorithms that can be used to treat the problems of making weighted approximations by sums of exponentials given equally or unequally spaced sampling. We apply the method to the case of missing data, although the above mentioned convergence results do not hold in this case. However, it turns out that the method often gives perfect reconstruction (up to machine precision) in such cases. We also discuss multidimensional extensions, and illustrate how the proposed algorithms can be used to recover sums of exponentials in several variables, but when samples are available only along a curve.

      PubDate: 2017-05-17T15:00:34Z
      DOI: 10.1016/j.acha.2017.03.004
  • Limits of calculating the finite Hilbert transform from discrete samples
    • Authors: Holger Boche; Volker Pohl
      Abstract: Publication date: Available online 21 March 2017
      Source:Applied and Computational Harmonic Analysis
      Author(s): Holger Boche, Volker Pohl
      This paper studies the problem of calculating the finite Hilbert transform f ˜ = H f of functions f from the set B of continuous functions with a continuous conjugate f ˜ based on discrete samples of f. It is shown that all sampling based linear approximations which satisfy three natural axioms diverge strongly on B in the uniform norm. More precisely, we consider sequences { H N } N ∈ N of linear approximation operators H N : B → B such that the calculation of H N f is based on discrete samples of f and which satisfies two additional natural axioms. We show that for all such sequences { H N } N ∈ N there always exists an f ∈ B such that lim N → ∞ ⁡ ‖ H N f ‖ ∞ = + ∞ . Moreover, it is shown that on the subset B 1 / 2 of all f ∈ B with finite Dirichlet energy an even larger class of sampling based approximation sequences diverges weakly, i.e. for all such sequences there always exists an f ∈ B 1 / 2 such that lim sup N → ∞ ‖ H N f ‖ ∞ = + ∞ .

      PubDate: 2017-05-17T15:00:34Z
      DOI: 10.1016/j.acha.2017.03.002
  • Sparse representation on graphs by tight wavelet frames and applications
    • Authors: Bin Dong
      Abstract: Publication date: May 2017
      Source:Applied and Computational Harmonic Analysis, Volume 42, Issue 3
      Author(s): Bin Dong
      In this paper, we introduce a new (constructive) characterization of tight wavelet frames on non-flat domains in both continuum setting, i.e. on manifolds, and discrete setting, i.e. on graphs; we discuss how fast tight wavelet frame transforms can be computed and how they can be effectively used to process graph data. We start with defining the quasi-affine systems on a given manifold M . The quasi-affine system is formed by generalized dilations and shifts of a finite collection of wavelet functions Ψ : = { ψ j : 1 ≤ j ≤ r } ⊂ L 2 ( R ) . We further require that ψ j is generated by some refinable function ϕ with mask a j . We present the condition needed for the masks { a j : 0 ≤ j ≤ r } , as well as regularity conditions needed for ϕ and ψ j , so that the associated quasi-affine system generated by Ψ is a tight frame for L 2 ( M ) . The condition needed for the masks is a simple set of algebraic equations which are not only easy to verify for a given set of masks { a j } , but also make the construction of { a j } entirely painless. Then, we discuss how the transition from the continuum (manifolds) to the discrete setting (graphs) can be naturally done. In order for the proposed discrete tight wavelet frame transforms to be useful in applications, we show how the transforms can be computed efficiently and accurately by proposing the fast tight wavelet frame transforms for graph data (WFTG). Finally, we consider two specific applications of the proposed WFTG: graph data denoising and semi-supervised clustering. Utilizing the sparse representation provided by the WFTG, we propose ℓ 1 -norm based optimization models on graphs for denoising and semi-supervised clustering. On one hand, our numerical results show significant advantage of the WFTG over the spectral graph wavelet transform (SGWT) by [1] for both applications. On the other hand, numerical experiments on two real data sets show that the proposed semi-supervised clustering model using the WFTG is overall competitive with the state-of-the-art methods developed in the literature of high-dimensional data classification, and is superior to some of these methods.

      PubDate: 2017-03-13T00:25:52Z
  • PROMP: A sparse recovery approach to lattice-valued signals
    • Authors: Axel Flinth; Gitta Kutyniok
      Abstract: Publication date: Available online 10 March 2017
      Source:Applied and Computational Harmonic Analysis
      Author(s): Axel Flinth, Gitta Kutyniok
      Applications such as wireless communications require efficient sensing techniques of signals with the a priori knowledge of those being lattice-valued. In this paper, we study the impact of this prior information on compressed sensing methodologies, and introduce and analyze PROMP (“PReprojected Orthogonal Matching Pursuit”) as a novel algorithmic approach for sparse recovery of lattice-valued signals. More precisely, we first show that the straightforward approach to project the solution of Basis Pursuit onto a prespecified lattice does not improve the performance of Basis Pursuit in this situation. We then introduce PROMP as a novel sparse recovery algorithm for lattice-valued signals which has very low computational complexity, alongside a detailed mathematical analysis of its performance and stability under noise. Finally, we present numerical experiments which show that PROMP outperforms standard sparse recovery approaches in the lattice-valued signal regime.

      PubDate: 2017-03-13T00:25:52Z
      DOI: 10.1016/j.acha.2016.12.004
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