Estimates for the best approximations and approximation by Fourier sums of classes of convolutions of periodic functions of not high smoothness in integral metrics
We obtain in the metric of spaces $L_{s}$, $1< s\leq\infty$, the exact order estimates of the best approximations and approximations by Fourier sums of classes of convolutions periodic functions that belong to unit ball of space $L_{1}$, with generating kernel $\Psi_{\beta}(t)=\sum_{k=1}^...
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| Date: | 2014 |
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| Keywords: | keywords |
| Main Authors: | , |
| Format: | Article |
| Language: | Ukrainian |
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Інститут математики НАН України
2014
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| Online Access: | https://trim.imath.kiev.ua/index.php/trim/article/view/80 |
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| Journal Title: | Transactions of Institute of Mathematics of NAS of Ukraine |
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Transactions of Institute of Mathematics of NAS of Ukraine| Summary: | We obtain in the metric of spaces $L_{s}$, $1< s\leq\infty$, the exact order estimates of the best approximations and approximations by Fourier sums of classes of convolutions periodic functions that belong to unit ball of space $L_{1}$, with generating kernel $\Psi_{\beta}(t)=\sum_{k=1}^{\infty}\psi(k)\cos\left(kt-\frac{\beta\pi}{2}\right)$, $\beta\in\mathbb{R}$. The kernel's coefficients $\psi(k)$ are such that product $\psi(n)n^{1-\frac{1}{s}}$, $1<s\leq\infty$, tends to zero not faster than an arbitrary power function and if $1<s<\infty$, then $\sum_{k=1}^{\infty}\psi^{s}(k)k^{s-2}<\infty$ and if $s=\infty$, then $\sum_{k=1}^{\infty}\psi(k)<\infty$ |
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