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High-dimensional Joint Sparsity Random Effects Model for Multi-task Learning
Proceedings of the 29th Conference on Uncertainty in Artificial Intelligence, PMLR R11:282-291, 2013.
Abstract
Joint sparsity regularization in multi-task learn- ing has attracted much attention in recent years. The traditional convex formulation employs the group Lasso relaxation to achieve joint sparsity across tasks. Although this approach leads to a simple convex formulation, it suffers from sev- eral issues due to the looseness of the relax- ation. To remedy this problem, we view jointly sparse multi-task learning as a specialized ran- dom effects model, and derive a convex relax- ation approach that involves two steps. The first step learns the covariance matrix of the coef- ficients using a convex formulation which we refer to as sparse covariance coding; the sec- ond step solves a ridge regression problem with a sparse quadratic regularizer based on the co- variance matrix obtained in the first step. It is shown that this approach produces an asymptot- ically optimal quadratic regularizer in the mul- titask learning setting when the number of tasks approaches infinity. Experimental results demon- strate that the convex formulation obtained via the proposed model significantly outperforms group Lasso (and related multi-stage formula- tions).