Blurb::
Have Surfpack compute a nugget to handle ill-conditioning
Description::
By default, the Surfpack GP handles ill-conditioning and does not use a nugget.
If the user wishes to specify a nugget, there are two approaches.

<ul>
  <li> The user can specify the value of a nugget with \ref model-surrogate-global-gaussian_process-surfpack-nugget.
  </li>
  <li> Have Surfpack find the optimal value of the nugget.
    This is specified by \ref model-surrogate-global-gaussian_process-surfpack-find_nugget.
    There are two options for find_nugget.
  </li>
  <ul>
    <li> \c find_nugget = 1: assume that the reciprocal condition number of the correlation
      matrix R, rcondR, is zero and calculate the nugget needed to make the worst case of
      R not ill-conditioned.
    </li>
    <li> \c find_nugget = 2: calculate rcondR,
      which requires a Cholesky factorization. If rcondR indicates that R is not
      ill-conditioned, then kriging uses the Cholesky factorization.
      Otherwise, if rcondR says R is ill conditioned, then kriging will calculate the
       nugget needed to make the worst case of R not ill conditioned.
    </li>
  </ul>
  \c find_nugget = 1 and 2 are similar, the second option just takes more computation
  (the initial Cholesky factorization) for larger problems.
  </li>
</ul>

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