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Re: AI-GEOSTATS: semivariogram for binary data

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  • Marco Alfaro
    Dear Malin: The semivariogram of an indicator variable is always less than 1. Proof: The experimental semivariogram is (1/2) of the mean of the squared
    Message 1 of 3 , Jan 16, 2001
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      Dear Malin:

      The semivariogram of an indicator variable is always less than 1.

      Proof:
      The experimental semivariogram is (1/2) of the mean of the squared
      differences Z(xi+h)-Z(xi) but the values of Z are 0 or 1, then the
      semivariogram is (1/2) of the mean of the absolutes values of
      Z(xi+h)-Z(xi). Now you use the triangular inequality and you get that
      the semivariogram is less than 1.

      Regards
      Marco Alfaro



      Malin Fahller wrote:

      > Hi everybody, I feel confused and really need some help to straighten
      > things out. I am currently working with geostatistical methods for
      > marine geological mapping. My sourcedata consists of sediment samples,
      > interpreted seismic profiles, bathymetric data and sonardata. In my
      > first, and easiest, case I only use the sedimentsamples to get a rough
      > picture of the sedimentary boundaries. So this question concerns the
      > use of one single source of data, sedimentary samples. The source data
      > is an ascii_file with three columns: (x_location, y_location, category
      > (i.e soiltype)). What I have done so far is that for each category
      > (i.e soiltype), I have done an indicator transform (for example:
      > value 1 = sand, value 0 = not sand). Then I have used GSLIB, gamv, to
      > make an omnidirectional semivariogram for my indicator transformed
      > data. This has worked really nicely but I get semivariogram values
      > that is larger than 1 and this troubles me. How can I possibly get
      > semivariogram values that is outside the range 0 - 1 when I have
      > indicator transformed data? Is there an error in the program or have I
      > misunderstood the mathematics of semivariograms? Can someone PLEASE
      > help me out. I reccon this is a basic question, but I just cant
      > proceed if I dont get this straightened out. Many thanks in
      > advanceMalin


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