Projections and Non-Linear Approximation in the Space BV($\mathbb{R}^d$)

• Autores: P. Wojtaszczyk
• Localización: Proceedings of the London Mathematical Society, ISSN 0024-6115, Vol. 87, Nº 2, 2003, págs. 471-497
• Idioma: inglés
• DOI: 10.1112/s0024611503014084
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• Resumen

  • The aim of this paper is to provide an analysis of non-linear approximation in the $L_p$-norm $p = d / (d - 1)$ of functions of bounded variation on $\mathbb{R}^d$ with $d > 1$ by polynomials in the Haar system. The exponent $p$ is the natural exponent as it is the correct exponent in the Sobolev inequality. The approximation schemes that we discuss in this paper are mostly related to Haar thresholding and $m$-term approximation. These problems for $d = 2$ are studied in detail in a paper by Cohen, DeVore, Petrushev and Xu. The main aim of this paper is to extend their results to the case $d \geq 2$.

    We obtain the optimal order of the $m$-term Haar approximation and prove the stability of Haar thresholding in the BV-norm. As one of the main tools, we establish the boundedness of certain averaging projections in BV.