Divergence conjecture for non-equidistant sampling in system approximation

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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 t∈Rt\in\mathbb{R}, there exist a stable LTI system T∗:PWπ1→PWπ1T_*:\mathcal{PW}_{\pi}^{1}\to\mathcal{PW}_{\pi}^{1} and a signal f∗∈PWσ1f_*\in\mathcal{PW}_{\sigma}^{1} such that

lim sup⁡N→∞∣(T∗f∗)(t)−∑k=−NNf∗(tk)(T∗ϕk)(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.

References

Primary source

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

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