Nonparametric Transforms of Graph Kernels for Semi-Supervised Learning
Xiaojin Zhu, Jaz Kandola, Zoubin Ghahramani and John Lafferty
In: NIPS, 13-18 Dec 2004, Vancouver, Canada.
We present an algorithm based on convex optimization for constructing kernels for semi-supervised learning. The kernel matrices are derived from the spectral decomposition of graph Laplacians, and combine labeled and unlabeled data in a systematic fashion. Unlike previous work using diffusion kernels and Gaussian random field kernels, a nonparametric kernel approach is presented that incorporates order constraints during optimization. This results in flexible kernels and avoids the need to choose among different parametric forms. Our approach relies on a quadratically constrained quadratic program (QCQP), and is computationally feasible for large datasets. We evaluate the kernels on real datasets using support vector machines, with encouraging results.