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15 - Learning Data-Driven Optimized Kernels

Published online by Cambridge University Press:  08 August 2026

Stefano De Marchi
Affiliation:
Università degli Studi di Padova, Italy
Francesco Marchetti
Affiliation:
Università degli Studi di Padova, Italy
Emma Perracchione
Affiliation:
Politecnico di Torino
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Summary

Standard kernels with scalar shape parameters lack flexibility for capturing anisotropic data structures in high dimensions. We present two-layered kernels built on a matrix transformation used to learn optimal feature directions. For Matérn kernels, we prove convergence rates depend on the effective dimension of this matrix, with faster rates when null space aligns with invariant subspaces of the target function. The 2L-KOGA algorithm combines kernel optimization via stochastic gradient descent with greedy node selection through VKOGA. Numerical experiments on regression benchmarks show 2L-KOGA outperforms standard kernels when significant dimensions can be reduced, with performance correlating to the concentration of singular values.

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