21 research outputs found

    The generic crystallographic phase retrieval problem

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    In this paper we consider the problem of recovering a signal xRNx \in \mathbb{R}^N from its power spectrum assuming that the signal is sparse with respect to a generic basis for RN\mathbb{R}^N. Our main result is that if the sparsity level is at most  ⁣N/2\sim\! N/2 in this basis then the generic sparse vector is uniquely determined up to sign from its power spectrum. We also prove that if the sparsity level is  ⁣N/4\sim\! N/4 then every sparse vector is determined up to sign from its power spectrum. Analogous results are also obtained for the power spectrum of a vector in CN\mathbb{C}^N which extend earlier results of Wang and Xu \cite{arXiv:1310.0873}.Comment: 20 page

    Phase retrieval with semi-algebraic and ReLU neural network priors

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    The key ingredient to retrieving a signal from its Fourier magnitudes, namely, to solve the phase retrieval problem, is an effective prior on the sought signal. In this paper, we study the phase retrieval problem under the prior that the signal lies in a semi-algebraic set. This is a very general prior as semi-algebraic sets include linear models, sparse models, and ReLU neural network generative models. The latter is the main motivation of this paper, due to the remarkable success of deep generative models in a variety of imaging tasks, including phase retrieval. We prove that almost all signals in R^N can be determined from their Fourier magnitudes, up to a sign, if they lie in a (generic) semi-algebraic set of dimension N/2. The same is true for all signals if the semi-algebraic set is of dimension N/4. We also generalize these results to the problem of signal recovery from the second moment in multi-reference alignment models with multiplicity free representations of compact groups. This general result is then used to derive improved sample complexity bounds for recovering band-limited functions on the sphere from their noisy copies, each acted upon by a random element of SO(3)
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