English

Two-dimensional Shannon type expansions via one-dimensional affine and wavelet lattice actions

Classical Analysis and ODEs 2016-12-19 v2

Abstract

It is rather unexpected, but true, that it is possible to construct reproducing formulae and orthonormal bases of L2(R2)L^2 (\mathbb{R}^2) just by applying the standard one dimensional wavelet action of translations and dilations to the first variable x1x_1 of the generating function ψ(x1,x2)\psi(x_1,x_2), ψL2(R2)\psi \in L^2 (\mathbb{R}^2), i.e., by making use of building blocks ψu,s(x1,x2)=s1/2ψ(x1us,x2),where uR,s>0,\psi_{u,s}(x_1,x_2)=s^{-1/2}\psi\left(\frac{x_1-u}{s},x_2\right), \text{where } u\in \mathbb{R}, s>0, in the case of reproducing formulae, and ψk,m(x1,x2)=2k/2ψ(x12km2k,x2),where k,mZ,\psi_{k,m}(x_1,x_2)=2^{-k/2} \psi\left(\frac{x_1-2^k m}{2^k},x_2 \right), \text{where } k,m\in \mathbb{Z}, in the case of orthonormal bases. It is possible to compensate the fact, that the second variable x2x_2 is not acted upon, by a careful selection of the generating function ψ\psi. Shannon wavelet tiling of the time-frequency plane R2\mathbb{R}^2, a standard illustration of orthogonality and completeness phenomena corresponding to the Shannon wavelet, χ(2km,2k(m+1)](x)χ2kI(ξ),k,mZ,I=(1/2,1](1/2,1], \chi_{(2^km,2^k(m+1)]}(x) \chi_{2^{-k}I}(\xi),\, k,m\in \mathbb{Z}, \,I=- (1/2,1]\cup (1/2,1], with xx representing time and ξ\xi frequency, is substituted by a phase space tiling of R4\mathbb{R}^4 with unbounded, hyperboloid type blocks of the form χ(2km,2k(m+1)](x1)n,lχ2kID(n,l)(ξ1)χ(n,n+1](x2)χ(l,l+1](ξ2),k,mZ \chi_{(2^km,2^k(m+1)]}(x_1)\sum_{n,l}\chi_{2^{-k}I_{D(n,l)}}(\xi_1) \chi_{(n,n+1]}(x_2)\chi_{(l,l+1]}(\xi_2),\, k,m\in \mathbb{Z} where Ir=2rII_r=2^{-r}I, r1 r\ge 1, and D:Z×ZND:\mathbb{Z} \times \mathbb{Z} \rightarrow \mathbb{N} is a bijection, an additional parameter of the generating function, needed for the lift from L2(R)L^2(\mathbb{R}) to L2(R2)L^2(\mathbb{R}^2). Variables x1,x2x_1,x_2 are coordinates of position and variables ξ1,ξ2\xi_1,\xi_2 of momentum.

Keywords

Cite

@article{arxiv.1611.05779,
  title  = {Two-dimensional Shannon type expansions via one-dimensional affine and wavelet lattice actions},
  author = {Krzysztof Nowak and Margit Pap},
  journal= {arXiv preprint arXiv:1611.05779},
  year   = {2016}
}