On Lipschitz Inversion of Nonlinear Redundant Representations

In this note we show that reconstruction from magnitudes of frame coefficients (the so called “phase retrieval problem”) can be performed us-ing Lipschitz continuous maps. Specifically we show that when the nonlin-ear analysis map α: H → Rm is injective, with (α(x))k = |〈x, fk〉|2, where {f1, · · · , fm} is a frame for the Hilbert space H, then there exists a left inverse map ω: Rm → H that is Lipschitz continuous. Additionally we obtain that the Lipschitz constant of this inverse map is at most 12 divided by the lower Lipschitz constant of α. 1.