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Article
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Colloquium Mathematicum
Article . 2004 . Peer-reviewed
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Good-λ inequalities for wavelets of compact support

Good-\(\lambda\) inequalities for wavelets of compact support
Authors: Cook, Sarah V.;

Good-λ inequalities for wavelets of compact support

Abstract

To a sequence \(a=\{a_J\}\) indexed by dyadic intervals \(J\) one can associate the square function \(S_\alpha(a)(x)=(\sum_{x\in \alpha J} | a_J| ^2/| J|)^{1/2}\). Here \(\alpha J\) is the interval with the same center and \(\alpha\) times the sidelength of \(J\). When \(\alpha=2\) one simply writes \(S(a)(x)\). A second maximal function can be defined in terms of the wavelet projection \(\Lambda_n(a)(x) =\sum_{| J| >2^{-n}} a_J \psi_J(x)\). When the wavelets \(\psi_J\) are generated by a multiresolution analysis, this is just the projection of \(\sum a_J\psi_J\) onto the \(n\)th multiresolution space. Then one can define \(N\Lambda(a)(x)=\sup_n \sup_{y\in J_n(x)}| \Lambda_n(y)| \). Here \(J_n(x)\) is the unique dyadic interval of length \(2^{-n}\) containing \(x\). Then \(N\Lambda\) is essentially the same as a nontangential maximal function and one expects the same sort of good-\(\lambda\) inequalities to govern \(S_\alpha\) and \(N\Lambda\) as those corresponding to the classical Littlewood-Paley square functions and standard nontangential maximal functions. Indeed, the main results (Theorems 3 and 4) are precisely such analogues. Theorem 3 says that \(S(a)\) cannot be small, too often, when \(N\Lambda(a)\) is large, that is, \[ | \{x\in\mathbb{R}:N\Lambda(a)(x)>k\lambda,\;S(a)(x)\lambda\}| \] for some fixed \(k>1\), provided \(\varepsilon>0\) is sufficiently small. Theorem 4 similarly says that \(N\Lambda(a)\) cannot be too small, too often, when \(S_\alpha(a)\) is too large. Here \(\alpha\) depends on the support of the wavelet.

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Keywords

relative distributional inequality, Maximal functions, Littlewood-Paley theory, square function, nontangential maximal function, Nontrigonometric harmonic analysis involving wavelets and other special systems, wavelets, multiresolution analysis

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selected citations
These citations are derived from selected sources.
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
1
Average
Average
Average
bronze