Papers › Learning Sparse Classifiers: Continuous and Mixed Integer Optimization Perspectives

Learning Sparse Classifiers: Continuous and Mixed Integer Optimization Perspectives

17 Jan 2020arXiv:2001.06471archive 2025-07-28

Antoine Dedieu, Hussein Hazimeh, Rahul Mazumder

We consider a discrete optimization formulation for learning sparse classifiers, where the outcome depends upon a linear combination of a small subset of features. Recent work has shown that mixed integer programming (MIP) can be used to solve (to optimality) ℓ₀-regularized regression problems at scales much larger than what was conventionally considered possible. Despite their usefulness, MIP-based global optimization approaches are significantly slower compared to the relatively mature algorithms for ℓ₁-regularization and heuristics for nonconvex regularized problems. We aim to bridge this gap in computation times by developing new MIP-based algorithms for ℓ₀-regularized classification. We propose two classes of scalable algorithms: an exact algorithm that can handle p≈50,000 features in a few minutes, and approximate algorithms that can address instances with p≈10⁶ in times comparable to the fast ℓ₁-based algorithms. Our exact algorithm is based on the novel idea of \textsl{integrality generation}, which solves the original problem (with p binary variables) via a sequence of mixed integer programs that involve a small number of binary variables. Our approximate algorithms are based on coordinate descent and local combinatorial search. In addition, we present new estimation error bounds for a class of ℓ₀-regularized estimators. Experiments on real and synthetic data demonstrate that our approach leads to models with considerably improved statistical performance (especially, variable selection) when compared to competing methods.

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