We propose a dimension reduction technique for Bayesian inverse problems with
nonlinear forward operators, non-Gaussian priors, and non-Gaussian observation
noise. The likelihood function is approximated by a ridge function, i.e., a map
which depends non-trivially only on a few linear combinations of the
parameters. We build this ridge approximation by minimizing an upper bound on
the Kullback--Leibler divergence between the posterior distribution and its
approximation. This bound, obtained via logarithmic Sobolev inequalities,
allows one to certify the error of the posterior approximation. Computing the
bound requires computing the second moment matrix of the gradient of the
log-likelihood function. In practice, a sample-based approximation of the upper
bound is then required. We provide an analysis that enables control of the
posterior approximation error due to this sampling. Numerical and theoretical
comparisons with existing methods illustrate the benefits of the proposed
methodology.

我们提出了一种用于贝叶斯反问题的降维技术，包括非线性正演算子、非高斯先验和非高斯观测噪声，我们通过一个垄线函数来近似似然函数，并最小化 KL 散度的上界来建立此垄线近似。这个上界可以通过对梯度的二阶矩矩阵的计算来获得并进行上界估计，数值和理论比较证明了方法的优点。