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An inexact successive quadratic approximation method for L-1 regularized optimization


We study a Newton-like method for the minimization of an objective function \(\phi \) that is the sum of a smooth function and an \(\ell _1\) regularization term. This method, which is sometimes referred to in the literature as a proximal Newton method, computes a step by minimizing a piecewise quadratic model \(q_k\) of the objective function \(\phi \). In order to make this approach efficient in practice, it is imperative to perform this inner minimization inexactly. In this paper, we give inexactness conditions that guarantee global convergence and that can be used to control the local rate of convergence of the iteration. Our inexactness conditions are based on a semi-smooth function that represents a (continuous) measure of the optimality conditions of the problem, and that embodies the soft-thresholding iteration. We give careful consideration to the algorithm employed for the inner minimization, and report numerical results on two test sets originating in machine learning.

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Corresponding author

Correspondence to Jorge Nocedal.

Additional information

To Jong-Shi Pang for his important contributions to optimization and his constant support.

Richard H. Byrd was supported by National Science Foundation Grant DMS-1216554 and Department of Energy Grant DE-SC0001774.

Jorge Nocedal was supported by National Science Foundation Grant DMS-0810213, and by ONR Grant N00014-14-1-0313 P00002.

Figen Oztoprak was supported by US Department of Energy Grant DE-FG02-87ER25047 and by Scientific and Technological Research Council of Turkey Grant Number 113M500. Part of this work was completed while the author was at Istanbul Technical University.

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Byrd, R.H., Nocedal, J. & Oztoprak, F. An inexact successive quadratic approximation method for L-1 regularized optimization. Math. Program. 157, 375–396 (2016).

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  • Sparse optimization
  • Inexact proximal Newton
  • Orthant-based quasi-Newton

Mathematics Subject Classification

  • 49M15
  • 90C55