Computer Science Department
School of Computer Science, Carnegie Mellon University


Fast Kernel Matrix-Vector Multiplication
with Application to Gaussian Process Learning

Alexander Gray

February 2004

Keywords: Gaussian processes, kernel matrix, matrix-vector multiplication, fast algorithms

A number of core computational problems in machine learning, both old and new, can be cast as a matrix-vector multiplication between a kernel matrix or class-probability matrix and a vector of weights. This arises prominently, for example, in the kernel estimation methods of nonparametric statistics, many common probabilistic graphical models, and the more recent kernel machines. After highlighting the existence of this computational problem in several well-known machine learning methods, we focus on a solution for one specific example for clarity, Gaussian process (GP) prediction -- one whose applicability has been particularly hindered by this computational barrier. We demonstrate the application of a recent N-body approach developed specifically for statistical problems, employing adaptive computational geometry and finite-difference approximation. This core algorithm reduces the O(N^2) matrix-vector multiplications within GP learning to O(N), making the resulting overall learning algorithm O(N). GP learning for N = 1 million points is demonstrated.

9 pages

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