Abstract
We develop conditions on a Sobolev function \(\psi \in W^{m,p}({\mathbb{R}}^d)\) such that if \(\widehat{\psi}(0) = 1\) and ψ satisfies the Strang–Fix conditions to order m − 1, then a scale averaged approximation formula holds for all \(f \in W^{m,p}({\mathbb{R}}^d)\) :
The dilations { a j } are lacunary, for example a j = 2j, and the coefficients c j,k are explicit local averages of f, or even pointwise sampled values, when f has some smoothness. For convergence just in \({W^{m - 1,p}({\mathbb{R}}^d)}\) the scale averaging is unnecessary and one has the simpler formula \(f(x) = \lim_{j \to \infty} \sum_{k \in {\mathbb{Z}}^d} c_{j,k}\psi(a_j x - k)\) . The Strang–Fix rates of approximation are recovered. As a corollary of the scale averaged formula, we deduce new density or “spanning” criteria for the small scale affine system \(\{\psi(a_j x - k) : j > 0, k \in {\mathbb{Z}}^d \}\) in \(W^{m,p}({\mathbb{R}}^d)\) . We also span Sobolev space by derivatives and differences of affine systems, and we raise an open problem: does the Gaussian affine system span Sobolev space?
Similar content being viewed by others
References
Adams R.A. (1975). Sobolev spaces. Academic, New York
Aldroubi A. and Feichtinger H.G. (1998). Exact iterative reconstruction algorithm for multivariate irregularly sampled functions in spline-like spaces: The L p-theory. Proc. Am. Math. Soc. 126: 2677–2686
Aldroubi A. and Gröchenig K. (2001). Nonuniform sampling and reconstruction in shift-invariant spaces. SIAM Rev. 43: 585–620
Babuška I. (1970). Approximation by hill functions. Comment Math. Univ. Carolinae 11: 787–811
Bui H.-Q. and Laugesen R.S. (2005). Affine systems that span Lebesgue spaces. J. Fourier Anal. Appl. 11: 533–556
Bui, H.-Q., Laugesen, R.S.: Spanning and sampling in Lebesgue and Sobolev spaces. University of Canterbury Research Report UCDMS2004/8, (2004). www.math.uiuc.edu/~laugesen/publications.html
Bui, H.-Q., Laugesen, R.S.: Approximation and spanning in the Hardy space, by affine systems. Constr Approx, appeared online (2007)
Bui, H.-Q., Laugesen, R.S.: Affine synthesis onto Lebesgue and Hardy spaces. Indiana Univ. Math. J. (2007) (to appear)
Bui, H.-Q., Paluszyński, M.: On the phi and psi transforms of Frazier and Jawerth. University of Canterbury Research Report UCDMS2004/11, 18 p (2004)
Casazza P.G. and Christensen O. (2001). Weyl–Heisenberg frames for subspaces of \(L^2({\mathbb{R}})\). Proc. Am. Math. Soc. 129: 145–154
Christensen, O.: An Introduction to Frames and Riesz Bases. Applied and Numerical Harmonic Analysis. Birkhäuser, Boston (2003)
Chui C.K. and Sun Q. (2006). Affine frame decompositions and shift-invariant spaces. Appl. Comput. Harmon Anal. 20: 74–107
Daubechies I. (1990). The wavelet transform, time–frequency localization and signal analysis. IEEE Trans. Inform. Theory 36: 961–1005
Filippov V.I. and Oswald P. (1995). Representation in L p by series of translates and dilates of one function. J. Approx. Th 82: 15–29
Fix G. and Strang G. (1969). Fourier analysis of the finite element method in Ritz–Galerkin theory. Stud. Appl. Math. 48: 265–273
Frazier, M., Jawerth, B., Weiss, G.: Littlewood-Paley theory and the study of function spaces. CBMS Reg Conf Ser in Math, No. 79. Amer. Math. Soc., Providence (1991)
Gilbert J.E., Han Y.S., Hogan J.A., Lakey J.D., Weiland D. and Weiss G. (2002). Smooth molecular decompositions of functions and singular integral operators. Memoirs Am. Math. Soc. 156(742): 74
Guglielmo F. (1969). Construction d’approximations des espaces de Sobolev sur des réseaux en simplexes. Calcolo 6: 279–331
Hernández E. and Weiss G. (1996). A First Course on Wavelets. CRC, Boca Raton
Holtz O. and Ron A. (2005). Approximation orders of shift-invariant subspaces of \(W^s_2({\mathbb{R}}^d)\). J. Approx. Theory 132: 97–148
Jetter K. and Zhou D.-X. (1997). Seminorm and full norm order of linear approximation from shift-invariant spaces. Rend. Sem. Mat. Fis. Milano 65(1995): 277–302
Jia R.-Q. (2004). Approximation with scaled shift-invariant spaces by means of quasi-projection operators. J. Approx. Theory 131: 30–46
Jia R.-Q., Wang J. and Zhou D.-X. (2003). Compactly supported wavelet bases for Sobolev spaces. Appl. Comput. Harmon Anal. 15: 224–241
Johnson M.J. (1997). On the approximation order of principal shift-invariant subspaces of L p(R d). J. Approx. Theory 91: 279–319
Laugesen, R.S.: Affine synthesis onto L p when 0 < p ≤ 1. J. Fourier Anal. Appl. (2007) (to appear)
Maz’ya V. and Schmidt G. (1996). On approximate approximations using Gaussian kernels. IMA J. Numer. Anal. 16: 13–29
Maz’ya V. and Schmidt G. (2001). On quasi-interpolation with non-uniformly distributed centers on domains and manifolds. J. Approx. Theory 110: 125–145
Meyer Y. (1992). Wavelets and Operators. Cambridge University Press, Cambridge
Mikhlin, S.G.: Approximation on a rectangular grid. Translated by R. S. Anderssen, T. O. Shaposhnikova. Sijthoff & Noordhoff, The Netherlands (1979)
Novak E. and Triebel H. (2006). Function spaces in Lipschitz domains and optimal rates of convergence for sampling. Constr. Approx. 23: 325–350
Schmidt, G.: Approximate approximations and their applications. In: The Maz’ya anniversary collection, Vol. 1 (Rostock, 1998), pp. 111–136. Oper Theory Adv Appl 109. Birkhäuser, Basel (1999)
Schoenberg, I.J.: Contributions to the problem of approximation of equidistant data by analytic functions. Parts A, B. Quart. Appl. Math. 4, 45–99, 112–141 (1946)
Strang, G.: The finite element method and approximation theory. In: Hubbard, B. (ed.) Numerical Solution of Partial Differential Equations, II (SYNSPADE 1970), pp. 547–583. Academic, New York (1971)
Strang, G., Fix, G.: A Fourier analysis of the finite element variational method. In: Geymonat, G. (ed.) Constructive Aspects of Functional Analysis, pp. 793–840. C.I.M.E. (1973)
Terekhin, P.A.: Inequalities for the components of summable functions and their representations by elements of a system of contractions and shifts. (Russian) Izv. Vyssh. Uchebn. Zaved. Mat. no. 8, 74–81 (1999); translation in Russian Math. (Iz. VUZ) 43(8), 70–77 (1999)
Terekhin P.A. (1999). Translates and dilates of function with nonzero integral (Russian). Math. Mech. (published by Saratov University) 1: 67–68
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Bui, HQ., Laugesen, R.S. Sobolev spaces and approximation by affine spanning systems. Math. Ann. 341, 347–389 (2008). https://doi.org/10.1007/s00208-007-0193-0
Received:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00208-007-0193-0