Definition of Term: Smoothness

The output of a simulator is regarded as a function of its inputs. One consideration in building an emulator for the simulator is whether the output is expected to be a smooth function of the inputs.

Smoothness might be measured formally in a variety of ways. For instance, we might refer to the expected number of times that the output crosses zero in a given range, or the expected number of local maxima or minima it will have in that range (which for a differentiable output corresponds to the number of times its derivative crosses zero). In the toolkit we do not adopt any specific measure of smoothness, but the concept is an important one.