Sparse Probability Regression by Label Partitioning
A large-margin learning machine for sparse probability regression is presented. Unlike support vector machines and other forms of kernel machines, nonlinear features are obtained by transforming labels into higher-dimensional label space rather than transforming data vectors into feature space. Linear multi-class logistic regression with partitioned classes of labels yields a nonlinear classifier in the original labels. With a linear kernel in data space, storage and run-time requirements are reduced from the number of support vectors to the number of partitioned labels. Using the partitioning property of KL-divergence in label space, an iterative alignment procedure produces sparse training coefficients. Experiments show that label partitioning is effective in modeling non-linear decision boundaries with same, and in some cases superior, generalization performance to Support Vector Machines with significantly reduced memory and run-time requirements.