Blurb:: A secondary rounding tolerance used for post-processing

Description::
After forming one or more function train approximations, this
tolerance is used for rolling up final results, in particular,
combining multilevel/multifidelity expansions and forming products for
higher-order moment estimation.  It is generally intended as a looser
tolerance than \c rounding_tolerance.

<b> Default Behavior </b>

If this tolerance is not specified, then we adopt the internal C3 default.

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See_Also:: model-surrogate-global-function_train-rounding_tolerance
