Blurb:: Construct moving least squares surrogate over active subspace

Description::

Once the active subspace variables have been identified, replace the
fullspace truth model with a moving least squares surrogate model over
the reduced variables.  The surrogate is constructed using the
fullspace function value samples collected during subspace
identification, possibly supplemented with additional \ref
model-active_subspace-build_surrogate-refinement_samples in the
fullspace.

<b> Default Behavior </b>

No surrogate is constructed by default.

Topics::

Examples::
\verbatim
model
  active_subspace
    id_model = 'SUBSPACE'
    actual_model_pointer = 'FULLSPACE'
    initial_samples  100
   build_surrogate
     refinement_samples 10
\endverbatim
Theory::
Faq::
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