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Compressed sensing
, 2004
"... We study the notion of Compressed Sensing (CS) as put forward in [14] and related work [20, 3, 4]. The basic idea behind CS is that a signal or image, unknown but supposed to be compressible by a known transform, (eg. wavelet or Fourier), can be subjected to fewer measurements than the nominal numbe ..."
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Cited by 3625 (22 self)
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We study the notion of Compressed Sensing (CS) as put forward in [14] and related work [20, 3, 4]. The basic idea behind CS is that a signal or image, unknown but supposed to be compressible by a known transform, (eg. wavelet or Fourier), can be subjected to fewer measurements than the nominal number of pixels, and yet be accurately reconstructed. The samples are nonadaptive and measure ‘random’ linear combinations of the transform coefficients. Approximate reconstruction is obtained by solving for the transform coefficients consistent with measured data and having the smallest possible `1 norm. We perform a series of numerical experiments which validate in general terms the basic idea proposed in [14, 3, 5], in the favorable case where the transform coefficients are sparse in the strong sense that the vast majority are zero. We then consider a range of lessfavorable cases, in which the object has all coefficients nonzero, but the coefficients obey an `p bound, for some p ∈ (0, 1]. These experiments show that the basic inequalities behind the CS method seem to involve reasonable constants. We next consider synthetic examples modelling problems in spectroscopy and image pro
For Most Large Underdetermined Systems of Linear Equations the Minimal ℓ1norm Solution is also the Sparsest Solution
 Comm. Pure Appl. Math
, 2004
"... We consider linear equations y = Φα where y is a given vector in R n, Φ is a given n by m matrix with n < m ≤ An, and we wish to solve for α ∈ R m. We suppose that the columns of Φ are normalized to unit ℓ 2 norm 1 and we place uniform measure on such Φ. We prove the existence of ρ = ρ(A) so that ..."
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Cited by 568 (10 self)
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We consider linear equations y = Φα where y is a given vector in R n, Φ is a given n by m matrix with n < m ≤ An, and we wish to solve for α ∈ R m. We suppose that the columns of Φ are normalized to unit ℓ 2 norm 1 and we place uniform measure on such Φ. We prove the existence of ρ = ρ(A) so that for large n, and for all Φ’s except a negligible fraction, the following property holds: For every y having a representation y = Φα0 by a coefficient vector α0 ∈ R m with fewer than ρ · n nonzeros, the solution α1 of the ℓ 1 minimization problem min �x�1 subject to Φα = y is unique and equal to α0. In contrast, heuristic attempts to sparsely solve such systems – greedy algorithms and thresholding – perform poorly in this challenging setting. The techniques include the use of random proportional embeddings and almostspherical sections in Banach space theory, and deviation bounds for the eigenvalues of random Wishart matrices.
FINDING STRUCTURE WITH RANDOMNESS: PROBABILISTIC ALGORITHMS FOR CONSTRUCTING APPROXIMATE MATRIX DECOMPOSITIONS
"... Lowrank matrix approximations, such as the truncated singular value decomposition and the rankrevealing QR decomposition, play a central role in data analysis and scientific computing. This work surveys and extends recent research which demonstrates that randomization offers a powerful tool for ..."
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Cited by 253 (6 self)
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Lowrank matrix approximations, such as the truncated singular value decomposition and the rankrevealing QR decomposition, play a central role in data analysis and scientific computing. This work surveys and extends recent research which demonstrates that randomization offers a powerful tool for performing lowrank matrix approximation. These techniques exploit modern computational architectures more fully than classical methods and open the possibility of dealing with truly massive data sets. This paper presents a modular framework for constructing randomized algorithms that compute partial matrix decompositions. These methods use random sampling to identify a subspace that captures most of the action of a matrix. The input matrix is then compressed—either explicitly or implicitly—to this subspace, and the reduced matrix is manipulated deterministically to obtain the desired lowrank factorization. In many cases, this approach beats its classical competitors in terms of accuracy, speed, and robustness. These claims are supported by extensive numerical experiments and a detailed error analysis. The specific benefits of randomized techniques depend on the computational environment. Consider the model problem of finding the k dominant components of the singular value decomposition
For most large underdetermined systems of equations, the minimal l1norm nearsolution approximates the sparsest nearsolution
 Comm. Pure Appl. Math
, 2004
"... We consider inexact linear equations y ≈ Φα where y is a given vector in R n, Φ is a given n by m matrix, and we wish to find an α0,ɛ which is sparse and gives an approximate solution, obeying �y − Φα0,ɛ�2 ≤ ɛ. In general this requires combinatorial optimization and so is considered intractable. On ..."
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Cited by 122 (1 self)
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We consider inexact linear equations y ≈ Φα where y is a given vector in R n, Φ is a given n by m matrix, and we wish to find an α0,ɛ which is sparse and gives an approximate solution, obeying �y − Φα0,ɛ�2 ≤ ɛ. In general this requires combinatorial optimization and so is considered intractable. On the other hand, the ℓ 1 minimization problem min �α�1 subject to �y − Φα�2 ≤ ɛ, is convex, and is considered tractable. We show that for most Φ the solution ˆα1,ɛ = ˆα1,ɛ(y, Φ) of this problem is quite generally a good approximation for ˆα0,ɛ. We suppose that the columns of Φ are normalized to unit ℓ 2 norm 1 and we place uniform measure on such Φ. We study the underdetermined case where m ∼ An, A> 1 and prove the existence of ρ = ρ(A) and C> 0 so that for large n, and for all Φ’s except a negligible fraction, the following approximate sparse solution property of Φ holds: For every y having an approximation �y − Φα0�2 ≤ ɛ by a coefficient vector α0 ∈ R m with fewer than ρ · n nonzeros, we have �ˆα1,ɛ − α0�2 ≤ C · ɛ. This has two implications. First: for most Φ, whenever the combinatorial optimization result α0,ɛ would be very sparse, ˆα1,ɛ is a good approximation to α0,ɛ. Second: suppose we are given noisy data obeying y = Φα0 + z where the unknown α0 is known to be sparse and the noise �z�2 ≤ ɛ. For most Φ, noisetolerant ℓ 1minimization will stably recover α0 from y in the presence of noise z. We study also the barelydetermined case m = n and reach parallel conclusions by slightly different arguments. The techniques include the use of almostspherical sections in Banach space theory and concentration of measure for eigenvalues of random matrices.
Finding structure with randomness: Stochastic algorithms for constructing approximate matrix decompositions
, 2009
"... Lowrank matrix approximations, such as the truncated singular value decomposition and the rankrevealing QR decomposition, play a central role in data analysis and scientific computing. This work surveys recent research which demonstrates that randomization offers a powerful tool for performing l ..."
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Cited by 62 (4 self)
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Lowrank matrix approximations, such as the truncated singular value decomposition and the rankrevealing QR decomposition, play a central role in data analysis and scientific computing. This work surveys recent research which demonstrates that randomization offers a powerful tool for performing lowrank matrix approximation. These techniques exploit modern computational architectures more fully than classical methods and open the possibility of dealing with truly massive data sets. In particular, these techniques offer a route toward principal component analysis (PCA) for petascale data. This paper presents a modular framework for constructing randomized algorithms that compute partial matrix decompositions. These methods use random sampling to identify a subspace that captures most of the action of a matrix. The input matrix is then compressed—either explicitly or implicitly—to this subspace, and the reduced matrix is manipulated deterministically to obtain the desired lowrank factorization. In many cases, this approach beats its classical competitors in terms of accuracy, speed, and robustness. These claims are supported by extensive numerical experiments and a detailed error analysis. The specific benefits of randomized techniques depend on the computational environment. Consider
A comparison principle for functions of a uniformly random subspace
"... Abstract This note demonstrates that it is possible to bound the expectation of an arbitrary norm of a random matrix drawn from the Stiefel manifold in terms of the expected norm of a standard Gaussian matrix with the same dimensions. A related comparison holds for any convex function of a random m ..."
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Abstract This note demonstrates that it is possible to bound the expectation of an arbitrary norm of a random matrix drawn from the Stiefel manifold in terms of the expected norm of a standard Gaussian matrix with the same dimensions. A related comparison holds for any convex function of a random matrix drawn from the Stiefel manifold. For certain norms, a reversed inequality is also valid. Mathematics Subject Classification (2010) Primary: 60B20 Main result Many problems in highdimensional geometry concern the properties of a random kdimensional subspace of the Euclidean space R n . For instance, the JohnsonLindenstrauss Lemma In geometric problems, it is often convenient to work with matrices rather than subspaces. Therefore, we introduce the Stiefel manifold,