Divergence conjecture for non-equidistant sampling in system approximation

Let t_k_{k\in\mathbb{Z}}\subset\mathbb{R} be an ordered complete interpolating sequence for PWπ2\mathcal{PW}_{\pi}^{2}, let ϕk\phi_k be as defined in the source, and let 0<σ<π0<\sigma<\pi. Divergence conjecture. For every tRt\in\mathbb{R}, there exist a stable LTI system T:PWπ1PWπ1T_*:\mathcal{PW}_{\pi}^{1}\to\mathcal{PW}_{\pi}^{1} and a signal fPWσ1f_*\in\mathcal{PW}_{\sigma}^{1} such that

lim supN(Tf)(t)k=NNf(tk)(Tϕk)(t)=.\limsup_{N\to\infty}\left|(T_*f_*)(t)-\sum_{k=-N}^{N}f_*(t_k)(T_*\phi_k)(t)\right|=\infty.

This conjecture asserts pointwise divergence of the digital approximation process for every complete interpolating sampling sequence; the paper states that it is proved in the cited section, so its database status is solved.

Sources & referencesView supporting material

Primary source

Holger Boche and Ullrich J. Mönich, “Signal and System Approximation from General Measurements”, arXiv:1402.1092 (2014).

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