Term, with Synonyms and Cross-References Definition Notes and Comments

reduced model
Synonym: emulator
A low-fidelity model developed to replace (or augment) a computationally demanding, high-fidelity model. A reduced model is particularly useful for carrying out computationally demanding analysis (e.g., sensitivity analysis, forward propagation of uncertainty, solving the inverse problem) that would be infeasible with the original model. Sometimes a reduced model “collapses” aspects of a “physics-based” model so as to be referred to as a “physics-blind” model.
See also: linear regression, nonlinear regression.
A form of statistical analysis in which observational data are used to statistically fit a mathematical function that presents the data (i.e., dependent variables) as a function of a set of parameters and one or more independent variables.  
response surface
See also sensitivity analysis.
A function that predicts outputs from a model as a function of the model inputs. A response surface is typically estimated from an ensemble of model runs using a regression, Gaussian process modeling, or some other estimation or interpolation procedure. A response surface can be used like a reduced model to carry out computationally demanding analyses (e.g., sensitivity analysis, forward propagation, solving the inverse problem). Since the response surface does not exactly reproduce the computational model, there is typically additional error in results produced by response surface approaches.
robustness analysis
See also sensitivity analysis.
For a prescriptive model, a procedure that analyzes the degree to which deviations from a “best” decision provide suboptimal values of the desired criterion. These deviations can be due to uncertainty in model formulation, assumed parameter values, etc.  
sensitivity analysis
See also robustness analysis.
An exploration, often by numerical (rather than analytical) means, of how model outputs (particularly QOIs) are affected by changes in the inputs (parameter values, assumptions, etc.).  
Synonym: model
See also Monte Carlo simulation.
The execution of a computer code to mimic an actual system. Many uncertainty quantification (UQ) methods use an ensemble of simulations, or model runs, to construct emulators, carry out sensitivity analysis, etc.
solution verification
See also verification, code verification.
The process of determining as completely as possible the accuracy with which the algorithms solve the mathematical-model equations for a specified QOI.  
standard deviation See also variance. The square root of the variance of a distribution.j  

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