Dakota variables can be grouped their type: \ref
topic-design_variables "design", uncertain (further sub-divided into
\ref topic-aleatory_uncertain_variables "aleatory" and \ref
topic-epistemic_uncertain_variables "epistemic"), and \ref
topic-state_variables "state".  These distinctions are useful in
situations where the user may want to explicitly control the subset of
variables that is considered \ref variables-active for a certain
%Dakota method, overriding the default active variable type.
