“…An equivalent statement to the above question is whether a signal f is determined, up to a sign, from the magnitude information |f (x)|, x ∈ D. The above question is an infinite-dimensional phase retrieval problem, which has been discussed for bandlimited signals [39], wavelet signals in a principal shift-invariant space [13,14,38], and spatial signals in a linear space [13]. The reader may refer to [1,2,8,20,27,28,33] for historical remarks and additional references on phase retrieval in an infinite-dimensional linear space.…”