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Subgradient methods for sharp weakly convex functions. (English) Zbl 1461.65140
Summary: Subgradient methods converge linearly on a convex function that grows sharply away from its solution set. In this work, we show that the same is true for sharp functions that are only weakly convex, provided that the subgradient methods are initialized within a fixed tube around the solution set. A variety of statistical and signal processing tasks come equipped with good initialization and provably lead to formulations that are both weakly convex and sharp. Therefore, in such settings, subgradient methods can serve as inexpensive local search procedures. We illustrate the proposed techniques on phase retrieval and covariance estimation problems.

65K05 Numerical mathematical programming methods
90C25 Convex programming
90C56 Derivative-free methods and methods using generalized derivatives
Wirtinger Flow
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