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Parameter-Free Spectral Kernel Learning
Proceedings of the 26th Conference on Uncertainty in Artificial Intelligence, PMLR R8:357-364, 2010.
Abstract
Due to the growing ubiquity of unlabeled data, learning with unlabeled data is attracting increas- ing attention in machine learning. In this paper, we propose a novel semi-supervised kernel learn- ing method which can seamlessly combine man- ifold structure of unlabeled data and Regularized Least-Squares (RLS) to learn a new kernel. Inter- estingly, the new kernel matrix can be obtained analytically with the use of spectral decomposi- tion of graph Laplacian matrix. Hence, the pro- posed algorithm does not require any numerical optimization solvers. Moreover, by maximizing kernel target alignment on labeled data, we can also learn model parameters automatically with a closed-form solution. For a given graph Lapla- cian matrix, our proposed method does not need to tune any model parameter including the trade- off parameter in RLS and the balance parame- ter for unlabeled data. Extensive experiments on ten benchmark datasets show that our proposed two-stage parameter-free spectral kernel learning algorithm can obtain comparable performance with fine-tuned manifold regularization methods in transductive setting, and outperform multiple kernel learning in supervised setting.