Reservoir Zero-Coordinatewise Projected Subspace Search for Minimization Over Sparse Symmetric Sets in Machine Learning
We study a class of nonconvex cardinality-constrained optimization problems arising in sparse learning. These problems are NP-hard due to the combinatorial nature of sparsity constraints. We introduce a Reservoir Zero-Coordinatewise Projected Subspace Search (RZCW-PSS) algorithm, a simplex-style method on sparse manifolds that integrates coordinatewise search, symmetry-aware swap-based support updates, randomized low-dimensional subspace exploration, and zero-coordinatewise reservoir injection. The proposed method augments classical coordinate and swap moves with sparse-compatible subspace searches constructed from a dynamically maintained reservoir of previously accepted feasible points. A key feature of the approach is a refined reservoir initialization strategy that embeds sparse projection directly into a uniform sampling procedure, preserving geometric diversity within the feasible set. The algorithm also includes an optional support-identification safeguard that enforces full-support stabilization under a fixed support-change decrease threshold. We establish that, under the stated regularity, sampling, and subproblem-accuracy assumptions, every full-support accumulation point of the RZCW-PSS iterates is Beck--Hallak zero-coordinatewise stationary almost surely; with the safeguard and full-support initialization, this conclusion applies to all accumulation points. We further prove a conditional local linear convergence rate after support stabilization and derive the corresponding logarithmic local iteration complexity. Numerical experiments on synthetic sparse learning problems demonstrate that RZCW-PSS improves robustness and solution quality while remaining computationally competitive with Partial Simplex Search, Basic Feasible Search, and Zero-Coordinatewise Search methods.