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GEOSTATS: gaussian and spherical variograms -Reply

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  • Sean A. McKenna
    A few comments in response to Don Myers recent mailing (I realize these are tangential to his main points, but I thought people might be interested): ... For a
    Message 1 of 1 , Sep 25, 1997
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      A few comments in response to Don Myers recent mailing (I realize these
      are tangential to his main points, but I thought people might be interested):

      Don wrote:

      >>It is well-known (although perhaps not written down anywhere)
      >>that it is best to use at least a small nugget with a Gaussian
      >>model otherwise the kriging coefficient matrix is likely to
      >>be ill-conditioned, making the results very unstable (numerically).

      For a reference that deals with this topic, check out:

      Ababou, Bagtzoglou and Wood, 1994, On the condition number of
      covariance matrices in kriging, estimation and simulation of random fields,
      Mathematical Geology, Vol. 26, No. 1, pp 99-133.

      Don also wrote:

      >>Note that some software does exactly that however, SURFER
      >>uses a linear variogram model and the slope of the model has no
      >>effect on the kriging weights (only on the kriging variances).

      Actually, Version 6 (1995) of SURFER allows for spherical, hole,
      exponential, gaussian, quadratic and rational quadratic models as well as
      the linear model. It is quite a sophisticated package these days.


      Sean A. McKenna
      Sandia National Laboratories ph: 505 848 0713
      Geohydrology Department fx: 505 848 0605
      PO Box 5800 MS 1324 em: samcken@...
      Albuquerque, NM 87185-1324
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