Gaussian processes are flexible function approximators, with inductive biases controlled by a covariance kernel. Learning the kernel is the key to representation learning and strong predictive performance. In this paper, we develop functional kernel learning (FKL) to directly infer functional posteriors over kernels. In particular, we place a transformed Gaussian process over a spectral density, to induce a non-parametric distribution over kernel functions. The resulting approach enables learning of rich representations, with support for any stationary kernel, uncertainty over the values of the kernel, and an interpretable specification of a prior directly over kernels, without requiring sophisticated initialization or manual intervention. We perform inference through elliptical slice sampling, which is especially well suited to marginalizing posteriors with the strongly correlated priors typical to function space modelling. We develop our approach for non-uniform, large-scale, multi-task, and multidimensional data, and show promising performance in a wide range of settings, including interpolation, extrapolation, and kernel recovery experiments.

本文提出了一种基于函数内核的学习方法（FKL），通过将高斯过程置于谱密度上，直接推断出内核的功能后验分布，从而能够支持任何平稳内核，具有对内核值的不确定性，以及直接对内核的先验规范，而不需要复杂的初始化或人为干预。我们通过椭圆切片采样进行推断，这对于较强相关性先验的函数空间建模尤其适用。我们将我们的方法应用于非均匀、大规模、多任务和多维数据，并在插值、外推和内核恢复实验中展现了良好的性能。

内核空间中的函数分布