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612Re: AI-GEOSTATS: Gaussian semivariogram model

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  • Pierre Goovaerts
    May 1, 2002
      Hello,

      Problems with the Gaussian semivariogram typically
      arise when no nugget effect is specified and
      some observations are very close to each other,
      leading to covariances matrice with very similar rows.
      You can read more about this "pathological" model in Hans
      Wackernagel's book "multivariate geostatistics"
      or the recent book by Chiles and Delfiner.

      Pierre
      <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>

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      On Wed, 1 May 2002, Soeren Nymand Lophaven wrote:

      > Dear list
      >
      > I have experienced that the gaussian semivariogram model sometimes leads
      > to a covariance matrix which is not positive definite. I am aware that the
      > parabolic behavior of the function near the origin could give these kinds
      > of problems, but I dont think this is the whole story. Do you about this
      > phenomenon, and where to read more about it ??
      >
      > Best regards / Venlig hilsen
      >
      > Søren Lophaven
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      > Informatics and Mathematical Modelling | Building 321, Room 011
      > Technical University of Denmark | 2800 kgs. Lyngby, Denmark
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      >
      >
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