Sandia National Laboratories

# Other Dakota Outputs

## Stochastic expansion exports

Polynomial chaos expansion (PCE) methods compute coefficients for response expansions which employ a basis of multivariate orthogonal polynomials. The `polynomial_chaos` method calculates these coefficients based on a number of stochastic expansion approaches. One may output the PCE coefficients to a file using the keyword `export_expansion_file = STRING`. Each row of the exported file will contain a coefficient, followed by the multi-index indicating which basis terms correspond to it. Only free-form format is supported for this file.

When using numerical integration schemes with structured rules, Dakota can also output the integration points and corresponding weights to a tabular file. This output is generated when `method` `output` is `verbose` or higher. Weights and points are printed to a file `dakota_quadrature_tabular.dat` (tensor product quadrature), `dakota_sparse_tabular.dat` (sparse grids), or `dakota_cubature_tabular.dat` (cubature methods), with one line per integration point.

## Surrogate Model Exports

Most Dakota surrogate models, including all those implemented in Surfpack, all those in the experimental surrogate module, and some stochastic expansion approaches support the keyword . When specified, any approximate evaluations performed on the surrogate model will be output to the specified data file. The data file can be exported in any of the tabular formats (default annotated). This facilitates plotting or external diagnostics of the surrogate model. Additionally, the Gaussian Process surrogate models can export variance predictions through .

In addition, the Surfpack and experimental families of global surrogate models can be exported to text and binary archives for later reuse in Dakota or other contexts, such as evaluation from C or Python, or with the `surfpack` executable or library API. Select Surfpack models can export to a human-readable and self-documenting algebraic form, suitable for reuse in user-developed tools. The keyword group for surfpack is used to specify model export filenames and formats.

## Variables Output from Pre-run

The pre-run mode (supported only for select methods) permits specification of an output file to which Dakota will write parameter (variables) data in any supported tabular data format (default annotated) with data columns corresponding to each variable. This file can be generated with sampling, parameter study, and DACE methods by invoking

    dakota -i dakota.in -pre_run ::variables.dat

for example, to output the variables (samples) in an LHS study. If a user adds the corresponding response values to this file, it may then be imported using Dakota’s post-run mode. Command line pre-run will always export in annotated format. To export pre-run data in other formats, specify `pre_run` in the input file instead of at the command-line, and provide a format option.

## Exceptional service in the national interest

© 2023 National Technology and Engineering Solutions of Sandia, LLC. | Questions & Comments | Privacy & Security

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525.