Blurb::
Output file for prediction variance calculations

Description::
Enables the user to specify the name and format of the file to which
corrected model variance information is output. The file will contain the 
values of the variances computed at those points specified with \c
num_predictions, \c prediction_configs, or \c import_prediction_configs.

For scalar responses, the prediction variance for each observable \f$d_i\f$ is 
calculated according to

\f[
\Sigma_{total}(x) = \Sigma_{\delta}(x) + \sigma^2_{exp}I.
\f]

Here, \f$\Sigma_{\delta}(x)\f$ is the (co)variance calculated from the
Gaussian process or polynomial regression model, details of which can be
found in the Dakota User's and Theory Manuals. If experimental variance
information is provided for the calibration, the maximum variance found for 
the observable \f$d_i\f$ is used as \f$\sigma^2_{exp}\f$. For more details, 
see the Dakota User's and Theory Manuals. For field responses, the variance 
of the discrepancy model alone is output to this file. 

<b> Default Behavior </b>

If \c export_corrected_variance_file is not specified, information will be 
automatically output to \c dakota_discrepancy_variance_tabular.dat.

<b> Usage Tips </b>

Dakota exports tabular data in one of three formats:
\li \c annotated (default)
\li \c custom_annotated
\li \c freeform

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