Gaussian process models -also called Kriging models- are often used as
mathematical approximations of expensive experiments. However, the number of
observation required for building an emulator becomes unrealistic when using
classical covariance kernels when the dimension of input increases. In oder to
get round the curse of dimensionality, a popular approach is to consider
simplified models such as additive models.
We study the class of Azema-Yor processes defined from a general
semimartingale with a continuous running supremum process. We show that they
arise as unique strong solutions of the Bachelier stochastic differential
equation which we prove is equivalent to the Drawdown equation. Solutions of
the latter have the drawdown property: they always stay above a given function
of their past supremum. We then show that any process which satisfies the
drawdown property is in fact an Azema-Yor process.