Emulating dynamic non-linear simulators using Gaussian processes
This provides a method for researchers in fields like climate science or neuroscience to efficiently analyze complex simulations, though it is incremental as it builds on existing Gaussian process emulation techniques.
The paper tackles the problem of emulating time-consuming non-linear deterministic simulators, such as climate or brain models, by using Gaussian processes to approximate their time series outputs, achieving relatively high predictive performance and accurate uncertainty measures in tests with Lorenz and Van der Pol equations.
The dynamic emulation of non-linear deterministic computer codes where the output is a time series, possibly multivariate, is examined. Such computer models simulate the evolution of some real-world phenomenon over time, for example models of the climate or the functioning of the human brain. The models we are interested in are highly non-linear and exhibit tipping points, bifurcations and chaotic behaviour. However, each simulation run could be too time-consuming to perform analyses that require many runs, including quantifying the variation in model output with respect to changes in the inputs. Therefore, Gaussian process emulators are used to approximate the output of the code. To do this, the flow map of the system under study is emulated over a short time period. Then, it is used in an iterative way to predict the whole time series. A number of ways are proposed to take into account the uncertainty of inputs to the emulators, after fixed initial conditions, and the correlation between them through the time series. The methodology is illustrated with two examples: the highly non-linear dynamical systems described by the Lorenz and Van der Pol equations. In both cases, the predictive performance is relatively high and the measure of uncertainty provided by the method reflects the extent of predictability in each system.