Blurb::
Variance applied to simulation responses  

Description::
The variance that is applied to simulations run by Dakota, i.e. using the
\c analysis_drivers command. The user may supply a single variance
or a vector of variances of length equal to the number of responses. In both 
cases, the values provided are treated as scalar variance types. If a single 
variance is provided, it is applied to all responses produced by the 
simulation code. If a vector is provided, each variance is applied to the
corresponding response output produced by the simulation code. 

It is important to note that the the variance defined by this keyword differs
from that defined using \c experiment_variance_type. These two commands apply 
to user-provided calibration data, specified, for example, by 
\c calibration_data or \c calibration_data_file. However, \c simulation_variance
applies to those responses produced by simulation code that is run by Dakota, 
as described above. 

<b> Usage Tips </b>

Currently, this keyword is only in use as part of the algorithm implemented by 
\ref method-bayes_calibration-experimental_design. In this algorithm, two
models (usually, one high-fidelity and one low-fidelity) are provided to 
Dakota, each with their own \c responses section of the input script, and each
of which is allowed its own \c simulation_variance. 
The variance specified in the \c responses 
block belonging to the high-fidelity model is applied to any <i> new </i> 
high-fidelity data that is produced by Dakota running the high-fidelity model.
In the \c experimental_design algorithm, 
low-fidelity model responses are used during the calibration of the model
parameters, the calculation of the mutual information, and the 
calculation of any posterior statistics after the algorithm is complete. The
\c simulation_variance is applied to the low-fidelity model responses that are
used in the calculation of the mutual information. See the User's and Theory 
Manuals for more information. 

Topics::	
Examples::
The example below shows two \c responses blocks, one for the low-fidelity 
model and one for the high-fidelity model. Both contain \c simulation_variance
commands that will apply to the low- and high-fidelity model responses,
respectively.

\verbatim
responses,
 	id_responses = 'low-fidelity'
	calibration_terms = 1
	simulation_variance = 0.5

responses,
 	id_responses = 'high-fidelity'
 	calibration_terms = 1
	calibration_data_file = 'dakota_bayes_expdesign.dat'	
	  freeform						
	  num_config_variables = 1				
	  num_experiments = 1				
	  experiment_variance_type = 'none'		
	simulation_variance = 1.2	
\endverbatim

Theory::
Faq::
See_Also::
