Abstract
One of the main results is a proposition to the effect that under some typically mild conditions finite sums of the form
are dense in an important sense in the set of shift-invariant approximately-finite-memory mapsG(·) that take a certain type of subsetU ofR intoR, whereR is the set of real-valued functions defined onR n orZ n. Here theQ m (·) are linear, σ is any element of a certain set of nonlinear maps fromR toR, and the κℓ, ρℓ, and ηℓm are real constants. Approximate representations comprising only affine elements and lattice nonlinearities are also presented.
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Sandberg, I.W. Structure theorems for nonlinear systems. Multidim Syst Sign Process 2, 267–286 (1991). https://doi.org/10.1007/BF01952236
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DOI: https://doi.org/10.1007/BF01952236