
doi: 10.1007/bf00971147
The author studies a correlation between the convergence of multiple Fourier series and corresponding multiple Fourier integral. For a \(2\pi\)- periodic function f(x), \(x\in R^ N\) with the Fourier decomposition \(\sum_{k}c_ ke^{ikx}\sim f(x),\) let us denote \[ S_ n(x;f)=\sum_{| k_ 1| \leq n_ 1}...\sum_{| k_ N| \leq n_ N}c_ ke^{i(k_ 1x_ 1+...+k_ Nx_ N)},\quad n=(n_ 1,n_ 2,...,n_ N)\in Z^ N, \] and for g(x)\(\sim \int_{R^ N}\hat g(y)e^{i(y,x)}dy\) let us denote \[ J_{\alpha}(x;g)=(2\pi)^{- N}\int^{\alpha_ 1}_{-\alpha_ 1}...\int^{\alpha_ N}_{- \alpha_ N}\hat g(y)e^{i(x,y)}dy,\quad \alpha \in R^ N_+. \] Theorem. There exist functions \(f\in L_ 1([-\pi,\pi]^ N)\), \(g\in L_ 1(R^ N)\), \(N\geq 2\) and for almost every \(x\in [-\pi,\pi]^ N\) there are sequences \(\{n(k,x)\}^{\infty}_{k=1}\) such that 1) \(f(x)=g(x)\), \(x\in [-\pi,\pi]^ N\); 2) (a) \(n(k,x)\in Z^ N\), (b) \(n_ 1(k,x)=n_ 2(k,x)=...=n_ N(k,x)=n_ 0(k,x)\), (c) \(0
convergence of multiple Fourier series, Fourier series and coefficients in several variables, multiple Fourier integral, Summability and absolute summability of Fourier and trigonometric series
convergence of multiple Fourier series, Fourier series and coefficients in several variables, multiple Fourier integral, Summability and absolute summability of Fourier and trigonometric series
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