Fully Polynomial-Time Randomized Approximation Schemes for Global Optimization of High-Dimensional Folded Concave Penalized Generalized Linear Models
Authors: Charles Hernandez, Hungyi Lee, Hongchen Liu
Keywords: statistical learning, FPRAS, global optimization, folded concave penalty, GLM, high dimensional learning
TL;DR: This paper primarily demonstrates a technique to find the global optima of FCP regularized GLMs which is to our knowledge the first of its kind.
Abstract: Global solutions to high-dimensional sparse estimation problems with a folded concave penalty (FCP) have been shown to be statistically desirable but are strongly  NP-hard to compute, which implies the non-existence of a pseudo-polynomial time global optimization schemes in the worst case. This paper shows that, with high probability, a global solution to the formulation for a FCP-based high-dimensional generalized linear model coincides with a stationary point characterized by the significant subspace second order necessary conditions (S$^3$ONC). Since the desired S$^3$ONC solution admits a fully polynomial-time approximation schemes (FPTAS), we thus have shown the existence of fully polynomial-time randomized approximation scheme (FPRAS) for a strongly NP-hard problem. We further demonstrate two versions of the FPRAS for generating the desired S$^3$ONC solutions. One follows the paradigm of an interior point trust region algorithm and the other is the well-studied local linear approximation (LLA).  Our analysis thus provides new techniques for global optimization of certain NP-Hard problems and new insights on the effectiveness of LLA.