Polyhedral summability of multiple Fourier series (and explicit formulas for Dirichlet kernels on $
Tom 65 / 1993
Colloquium Mathematicum 65 (1993), 103-116
DOI: 10.4064/cm-65-1-103-116
Streszczenie
We study polyhedral Dirichlet kernels on the n-dimensional torus and we write a fairly simple formula which extends the one-dimensional identity $∑_{j=-N}^N e^{ijt} = sin((N+(1/2))t) / sin((1/2)t)$. We prove sharp results for the Lebesgue constants and for the pointwise boundedness of polyhedral Dirichlet kernels; we apply our results and methods to approximation theory, to more general summability methods and to Fourier series on compact Lie groups, where we write an asymptotic formula for the Dirichlet kernels.
