We provide a unifying framework linking two classes of statistics used in
two-sample and independence testing: on the one hand, the energy distances and
distance covariances from the statistics literature; on the other, distances
between embeddings of distributions to reproducing kernel Hilbert spaces
(RKHS), as established in machine learning. The equivalence holds when energy
distances are computed with semimetrics of negative type, in which case a
kernel may be defined such that the RKHS distance between distributions
corresponds exactly to the energy distance.
Discussion on "Brownian distance covariance" by G\'{a}bor J. Sz\'{e}kely and
Maria L. Rizzo [arXiv:1010.0297]
A kernel method is proposed for realizing Bayes' rule, based on
representations of probability distributions in reproducing kernel Hilbert
spaces (RKHS). The empirical RKHS embeddings of the conditional probabilities
and prior are expressed as feature mappings of samples, and an RKHS embedding
of the posterior distribution is computed, again based on a feature mapping of
a sample. This kernel Bayes' rule can be applied to a wide variety of
nonparametric Bayesian inference problems. As an example, the approach is used
in filtering with a nonparametric state-space model.
A class of distance measures on probabilities -- the integral probability
metrics (IPMs) -- is addressed: these include the Wasserstein distance, Dudley
metric, and Maximum Mean Discrepancy. IPMs have thus far mostly been used in
more abstract settings, for instance as theoretical tools in mass
transportation problems, and in metrizing the weak topology on the set of all
Borel probability measures defined on a metric space.