Let S be the space of rapidly
decreasing indefinitely differentiable functions on the n-dimensional Euclidean
space Rn, and suppose that ϕ ∈ S. We attempt to characterize the closed
vector subspace of S which is generated by the set of all functions of the
form
where a1,⋯,an,b1,⋯,bn are real numbers, with a1,⋯,an nonzero. We also consider
an analogous approximation problem in the space S′ of temperate distribution on
Rn.
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