About SEPIA¶
The general motivation for this project is the analysis of computer models, and the analysis of systems that have both computer simulations and observed data. The underlying assumption is that experimental results are expensive or difficult to collect, though it is possible to get simulation studies of the experimental problem in comparatively large, but still restricted, quantities. Therefore a statistical model of system responses is to be constructed, which is called a surrogate or emulator.
The emulator is constructed from an ensemble of simulation responses collected at various settings of input parameters. The statistical model may be extended to incorporate system observations to improve system predictions and constrain, or calibrate, unknown parameters. The statistical model accounts for the discrepancy between the system observations and the simulation output. Parameters of the statistical model are determined through sampling their posterior probability with MCMC. The statistical model can then be used in several ways. Statistical prediction of simulation and observation response is relatively fast and includes uncertainty. Examination and analysis of the model parameters can be used for calibration, screening, and analysis of model properties. The emulator may be further used for sensitivity analysis, and other system diagnostics.
Before using the SEPIA package, the analysis problem will have been defined, including: collecting system observations; determining uncertain simulation parameters; establishing a design over the simulation parameters and running an ensemble of simulations; considering an appropriate model for dimension reduction of the observation and simulation response; considering an appropriate model for the discrepancy between simulation and observation; and considering prior model parameter settings related to these issues.
The SEPIA code is developed and maintained by the CCS-6 group at Los Alamos National Laboratory.
How should one pronounce Sepia?
This is a topic of some debate. This video suggests “see-pee-uh”.
Approved by LANL/NNSA for software release: C19159 SEPIA
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