Convergence of Greedy Approximation for the Trigonometric SystemVladimir Temlyakov given at strobl07 (20.06.07 11:00) id: 671 length: 50min status: invited type: talk LINK-Presentation: http://univie.ac.at/nuhag-php/dateien/talks/671_Wconf.pdf ABSTRACT: TeX: We study the following nonlinear method of approximation by trigonometric polynomials. For a periodic function $f$ we take as an approximant a trigonometric polynomial of the form $G_m(f) := \sum_{k \in \Lambda} \hat f(k) e^{i(k,x)} $, where $\Lambda \subset \Bbb Z^d$ is a set of cardinality $m$ containing the indices of the $m$ biggest (in absolute value) Fourier coefficients $\hat f(k)$ of function $f$. Note that $G_m(f)$ gives the best $m$-term approximant in the $L_2$-norm and, therefore, for each $f\in L_2$, $\|f-G_m(f)\|_2 \to 0$ as $m\to \infty$. It is known from previous results that in the case of $p\neq 2$ the condition $f\in L_p$ does not guarantee the convergence $\|f-G_m(f)\|_p \to 0$ as $m\to \infty$. We study the following question. What conditions (in addition to $f\in L_p$) provide the convergence $\|f-G_m(f)\|_p \to 0$ as $m\to \infty$? |