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Poster

Escaping Saddle Points in Constrained Optimization

Aryan Mokhtari · Asuman Ozdaglar · Ali Jadbabaie

Room 210 #47

Keywords: [ Non-Convex Optimization ] [ Computational Complexity ]


Abstract: In this paper, we study the problem of escaping from saddle points in smooth nonconvex optimization problems subject to a convex set C. We propose a generic framework that yields convergence to a second-order stationary point of the problem, if the convex set C is simple for a quadratic objective function. Specifically, our results hold if one can find a ρ-approximate solution of a quadratic program subject to C in polynomial time, where ρ<1 is a positive constant that depends on the structure of the set C. Under this condition, we show that the sequence of iterates generated by the proposed framework reaches an (ϵ,γ)-second order stationary point (SOSP) in at most O(max{ϵ2,ρ3γ3}) iterations. We further characterize the overall complexity of reaching an SOSP when the convex set C can be written as a set of quadratic constraints and the objective function Hessian has a specific structure over the convex C. Finally, we extend our results to the stochastic setting and characterize the number of stochastic gradient and Hessian evaluations to reach an (ϵ,γ)-SOSP.

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