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AI-GEOSTATS: SA using GSLIB

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  • Uwe Haberlandt
    Dear all, I have a question concerning the simulated annealing module within GSLIB (f77v2 and f90). I m using kilometers as units with grid spacing of 0.5 km
    Message 1 of 2 , Jun 13, 2003
      Dear all,

      I have a question concerning the simulated annealing module within GSLIB
      (f77v2 and f90). I'm using kilometers as units with grid spacing of 0.5
      km and wanted a reproduction of the variogram up to a distance of 20 km.
      The range is 10 km. However for different nlags set in the parameter
      file (e.g. 20, 40, 80,120) the debugging file reports variogram values
      (actual and model) much lower than expected. In the debugging file the
      model variogram does not reach the sill not even with nlags=120. How is
      "nlags" interpreted and what is reported in the debug file?

      Any help is greatly appreciated
      Regards
      Uwe


      **********************************************************
      Dr. Uwe Haberlandt
      Ruhr University Bochum
      Institute for Hydrology, Water Management
      and Environmental Engineering
      Universitätsstraße 150
      44780 Bochum
      Germany
      Tel.: +49 (0)234-32-27619
      Fax.: +49 (0)234-32-14153
      e-mail: uwe.haberlandt@...
      www: http://www.ruhr-uni-bochum.de/hydrology/
      **********************************************************



      [Non-text portions of this message have been removed]
    • Pierre Goovaerts
      Dear Uwe, The interpretation of the nlag parameter in sasim can be somewhat confusing. It corresponds to the number of lags in all directions to be
      Message 2 of 2 , Jun 13, 2003
        Dear Uwe,

        The interpretation of the nlag parameter in sasim
        can be somewhat confusing. It corresponds to the number
        of lags in all directions to be incorporated in the objective
        functions, not the class of distance for the semivariogram
        model. For example, to reproduce the variogram for
        the 1st "lag distance" of 0.5 km in all directions,
        you need to specify nlags=8, which corresponds to
        the number of cells in the direct neighborhood of the cell
        being simulated. For reproducing the 2nd class of distance
        of 1km, nlags should be 24. So the formula to use to
        reproduce K classes of distances would be
        nlag=[(2K+1)^2]-1. So if you want to reproduce the variogram
        up to a distance of 20 kms using a grid size of 0.5km
        nlag=[(2x40+1)^2]-1=6560! I have recently looked at ways
        to sample this set of lags since it is clearly impossible
        to afford such a large number of lags in the objective function.
        For example, only a random subset of these 6,560 possible lags
        would be reproduced. This is a limitation of the simulated annealing
        algorithm (would be even worst in 3D) and any other suggestions
        would be much appreciated.

        Regards,

        Pierre Goovaerts

        <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>

        Dr. Pierre Goovaerts
        President of PGeostat, LLC
        Chief Scientist with Biomedware Inc.
        710 Ridgemont Lane
        Ann Arbor, Michigan, 48103-1535, U.S.A.

        E-mail: goovaert@...
        Phone: (734) 668-9900
        Fax: (734) 668-7788
        http://alumni.engin.umich.edu/~goovaert/

        <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>

        On Fri, 13 Jun 2003, Uwe Haberlandt wrote:

        > Dear all,
        >
        > I have a question concerning the simulated annealing module within GSLIB
        > (f77v2 and f90). I'm using kilometers as units with grid spacing of 0.5
        > km and wanted a reproduction of the variogram up to a distance of 20 km.
        > The range is 10 km. However for different nlags set in the parameter
        > file (e.g. 20, 40, 80,120) the debugging file reports variogram values
        > (actual and model) much lower than expected. In the debugging file the
        > model variogram does not reach the sill not even with nlags=120. How is
        > "nlags" interpreted and what is reported in the debug file?
        >
        > Any help is greatly appreciated
        > Regards
        > Uwe
        >
        >
        > **********************************************************
        > Dr. Uwe Haberlandt
        > Ruhr University Bochum
        > Institute for Hydrology, Water Management
        > and Environmental Engineering
        > Universitätsstraße 150
        > 44780 Bochum
        > Germany
        > Tel.: +49 (0)234-32-27619
        > Fax.: +49 (0)234-32-14153
        > e-mail: uwe.haberlandt@...
        > www: http://www.ruhr-uni-bochum.de/hydrology/
        > **********************************************************
        >
        >


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