Discrete versus Continuous Time-Frequency (and Gabor) AnalysisHans G. Feichtinger (NuHAG (University of Vienna) and ARI (OEAW)) given at (10.04.25 12:15) id: 3747 length: 45min status: type: LINK-Presentation: https://nuhagphp.univie.ac.at/dateien/talks/3747_FeiHasen25A01.pdf ABSTRACT: The regular sampling problem is usually related to classical work of Shannon, who has shown that band-limited functions in $L^2(R)$ can be reconstructed from their regular samples, if the Nyquist criterion is satisfied. There are many variations to this theme, taking other function spaces into account, which allow to grasp better the locality of the reconstruction, or even reconstruct from irregular samples, using iterative methods. For me {\it Wiener amalgam spaces} are the natural setting, because they provide methods to control the convergence in different function spaces or control jitter errors. The early work on sampling by Paul Butzer clearly shows the close connection to Poisson's formula. It results in the statement that the Dirac comb (viewed as a mild distribution) has the Dirac comb of the dual lattice as its Fourier transform. Thus sampling on the time side corresponds to periodization on the frequency side. For this way of looking at sampling we may use the Banach Gelfand triple $(SO,L2,SO^*)$, which arose in time-frequency analysis. The talk will discuss a few topics closely connected to the question whether a function in $SO(R)$ can be approximately reconstructed from regular samples, if they are taken over a sufficiently fine grid and over a sufficiently large interval. The approach takes a combined periodization sampling operator as the starting point and starts the analysis by looking at its spreading representation. Obviously it can be viewed as a mapping from $SO(R)$ into $C^N$ \newline (for sufficiently large $N$), or equivalently as a bounded linear mapping from $SO(R)$ into $SO^*(R)$. A corresponding paper is under preparation. |