CMS/SMC
Canadian Mathematical Society
www.cms.math.ca
Canadian Mathematical Society
  location:  PublicationsjournalsCMB
Publications        
Abstract view

On $L^{1}$-Convergence of Fourier Series under the MVBV Condition

  Published:2009-12-01
 Printed: Dec 2009
  • Dan Sheng Yu
  • Ping Zhou
  • Song Ping Zhou
Features coming soon:
Citations   (via CrossRef) Tools: Search Google Scholar:
Format:   HTML   LaTeX   MathJax   PDF   PostScript  

Abstract

Let $f\in L_{2\pi }$ be a real-valued even function with its Fourier series $% \frac{a_{0}}{2}+\sum_{n=1}^{\infty }a_{n}\cos nx,$ and let $S_{n}(f,x) ,\;n\geq 1,$ be the $n$-th partial sum of the Fourier series. It is well known that if the nonnegative sequence $\{a_{n}\}$ is decreasing and $\lim_{n\rightarrow \infty }a_{n}=0$, then% \begin{equation*} \lim_{n\rightarrow \infty }\Vert f-S_{n}(f)\Vert _{L}=0 \text{ if and only if }\lim_{n\rightarrow \infty }a_{n}\log n=0. \end{equation*}% We weaken the monotone condition in this classical result to the so-called mean value bounded variation (MVBV) condition. The generalization of the above classical result in real-valued function space is presented as a special case of the main result in this paper, which gives the $L^{1}$% -convergence of a function $f\in L_{2\pi }$ in complex space. We also give results on $L^{1}$-approximation of a function $f\in L_{2\pi }$ under the MVBV condition.
Keywords: complex trigonometric series, $L^{1}$ convergence, monotonicity, mean value bounded variation complex trigonometric series, $L^{1}$ convergence, monotonicity, mean value bounded variation
MSC Classifications: 42A25, 41A50 show english descriptions unknown classification 42A25
Best approximation, Chebyshev systems
42A25 - unknown classification 42A25
41A50 - Best approximation, Chebyshev systems
 

© Canadian Mathematical Society, 2014 : http://www.cms.math.ca/