This paper presents a new method for the selection of the two hyperparameters of Least Squares Support Vector Machine (LS-SVM) approximators with Gaussian Kernels. The two hyperparameters are the width sigma of the Gaussian kernels and the regularization parameter lambda. For different values of sigma, a Nonparametric Noise Estimator (NNE) is introduced to estimate the variance of the noise on the outputs. The NNE allows the determination of the best lambda for each given sigma. A Leave-one-out methodology is then applied to select the best sigma. Therefore, this method transforms the double optimization problem into a single optimization one. The method is tested on 2 problems: a toy example and the Pumadyn regression Benchmark.
Lendasse, A., Ji, J., Reyhani, N., & Verleysen, M. (2005). LS-SVM hyperparameter selection with a nonparametric noise estimator. Lecture Notes in Computer Science, 3697, 625-630. https://hdl.handle.net/2078.5/254011 (Original work published 2005)