Cameron-Martin space
Definition 1.
Let be Wiener space. The Cameron-Martin space is the subspace of consisting of all paths such that is absolutely continuous and . (Note that if is absolutely continuous, then it is almost everywhere differentiable
, so the integral makes sense.)
This can be thought of as the set of paths with “finite energy.”
Note that has Wiener measure , since sample paths of Brownian motion are nowhere differentiable, whereas a path from is almost everywhere differentiable.