Kernel regression is an essential and ubiquitous tool for non-parametric data analysis, particularly popular among time series and spatial data. However, the central operation which is performed many times, evaluating a kernel on the data set, takes linear time. This is impractical for modern large data sets. In this paper we describe coresets for kernel regression: compressed data sets which can be used as proxy for the original data and have provably bounded worst case error. The size of the coresets are independent of the raw number of data points, rather they only depend on the error guarantee, and in some cases the size of domain and amount of smoothing. We evaluate our methods on very large time series and spatial data, and demonstrate that they incur negligible error, can be constructed extremely efficiently, and allow for great computational gains.
This is the first work to address sample complexity and coreset size for Nadaraya-Watson kernel regression. There is an enormous body of work on other types of coresets, see the recent survey on coresets @cite_23 , including many for parametric regression variants like least-square regression @cite_19 and @math regression @cite_7 .
@cite_19 @cite_7 @cite_23
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We consider supervised learning problems within the positive-definite kernel framework, such as kernel ridge regression, kernel logistic regression or the support vector machine. With kernels leading to infinite-dimensional feature spaces, a common practical limiting difficulty is the necessity of computing the kernel matrix, which most frequently leads to algorithms with running time at least quadratic in the number of observations n, i.e., O(n^2). Low-rank approximations of the kernel matrix are often considered as they allow the reduction of running time complexities to O(p^2 n), where p is the rank of the approximation. The practicality of such methods thus depends on the required rank p. In this paper, we show that in the context of kernel ridge regression, for approximations based on a random subset of columns of the original kernel matrix, the rank p may be chosen to be linear in the degrees of freedom associated with the problem, a quantity which is classically used in the statistical analysis of such methods, and is often seen as the implicit number of parameters of non-parametric estimators. This result enables simple algorithms that have sub-quadratic running time complexity, but provably exhibit the same predictive performance than existing algorithms, for any given problem instance, and not only for worst-case situations. We consider supervised learning problems within the positive-definite kernel framework, such as kernel ridge regression, kernel logistic regression or the support vector machine. With kernels leading to infinite-dimensional feature spaces, a common practi cal limiting difficulty is the necessity of computing the kernel matrix, which most frequently leads to algorithms with running time at least quadratic in the number of observations n, i.e., O(n 2 ). Low-rank approximations of the kernel matrix are often considered as they allow the reduction of running time complexities to O(p 2 n), where p is the rank of the approximation. The practicality of such methods thus depends on the required rank p. In this paper, we show that in the context of kernel ridge regression, for approximations based on a random subset of columns of the original kernel matrix, the rank p may be chosen to be linear in the degrees of freedom associated with the problem, a quantity which is classically used in the statistical analysis of such method s, and is often seen as the implicit number of parameters of non-parametric estimators. This result enables simple algorithms that have sub-quadratic running time complexity, but provably exhibit the same predictive performancethan existing algorithms, for any given problem instance, and not only for worst-case situations. A rigid coreset minimum enclosing ball training machine for kernel regression estimation was proposed. First, it transfers the kernel regression estimation machine problem into a center-constrained minimum enclosing ball representation form, and subsequently trains the kernel methods using the proposed MEB algorithm. The primal variables of the kernel methods are recovered via KKT conditions. Then, detailed theoretical analysis and main theoretical results of our new algorithm are given. It can be concluded that our proposed MEB training algorithm is independent of sample dimension and the time complexity is linear in sample numbers, which greatly cuts down the complexity level and is expected to speedup the learning process obviously. Finally, comments about the future development directions are discussed. The problem of learning several related tasks has recently been addressed with success by the so-called multi-task formulation, that discovers underlying common structure between tasks. Metric Learning for Kernel Regression (MLKR) aims at finding the optimal linear subspace for reducing the squared error of a Nadaraya-Watson estimator. In this paper, we propose two Multi-Task extensions of MLKR. The first one is a direct application of multi-task formulation to MLKR algorithm and the second one, the so-called Hard-MT-MLKR, lets us learn same-complexity predictors with fewer parameters, reducing overfitting issues. We apply the proposed method to Action Unit (AU) intensity prediction as a response to the Facial Expression Recognition and Analysis challenge (FERA'15). Our system improves the baseline results on the test set by 24 in terms of Intraclass Correlation Coefficient (ICC).