Optimizing Sparse Kernel Ridge Regression hyperparameters based on leave-one-out cross-validation

Kernel Ridge Regression (KRR) is a nonlinear extension of the ridge regression. The performance of the KRR depends on its hyperparameters such as a penalty factor C, and RBF kernel parameter σ. We employ a method called MCV-KRR which optimizes the KRR hyperparameters so that a cross-validation error is minimized. This method becomes equivalent to a predictive approach to Gaussian Process. Since the cost of KRR training is O(N³) where N is a data size, to reduce this complexity, some sparse approximation of the KRR is recently studied. In this paper, we apply the minimum cross-validation (MCV) approach to such sparse approximation. Our experiments show the MCV with the sparse approximation of the KRR can achieve almost the same generalization performance as the MCV-KRR with much lower cost.