Title: How Deep Are Deep Gaussian Processes?,
Abstract: Recent research has shown the potential utility of Deep Gaussian Processes.
These deep structures are probability distributions, designed through
hierarchical construction, which are conditionally Gaussian. In this paper, the
current published body of work is placed in a common framework and, through
recursion, several classes of deep Gaussian processes are defined. The
resulting samples generated from a deep Gaussian process have a Markovian
structure with respect to the depth parameter, and the effective depth of the
resulting process is interpreted in terms of the ergodicity, or non-ergodicity,
of the resulting Markov chain. For the classes of deep Gaussian processes
introduced, we provide results concerning their ergodicity and hence their
effective depth. We also demonstrate how these processes may be used for
inference; in particular we show how a Metropolis-within-Gibbs construction
across the levels of the hierarchy can be used to derive sampling tools which
are robust to the level of resolution used to represent the functions on a
computer. For illustration, we consider the effect of ergodicity in some simple
numerical examples.