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AI-GEOSTATS: negative weight

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  • lfontaine@cogema.fr
    Hi Mailinglist!!! I have got some problems with negative weight in my cokriging, they induce negative grade. Have you got some advice or publication to help
    Message 1 of 5 , Sep 4, 2003
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      Hi Mailinglist!!!

      I have got some problems with negative weight in my cokriging, they induce
      negative grade. Have you got some advice or publication to help me.I hope
      you can help me with some of your answers.

      Thank

      Laure



      Laure FONTAINE
      Services des Réserves
      COGEMA BUM/DT
      tél: 33 1 39 26 32 05
      Fax: 33 1 39 26 27 31



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    • Isobel Clark
      Laure You will probably get lots of replies on this and plenty of references, so I will stick to what I know. Possible reasons for large negative weights: (a)
      Message 2 of 5 , Sep 4, 2003
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        Laure

        You will probably get lots of replies on this and
        plenty of references, so I will stick to what I know.
        Possible reasons for large negative weights:

        (a) samples are too close together with low nugget
        effects on the semi-variogram models. This leads to
        precision problems in solving the equations for the
        kriging and gives unstable results

        (b) the nugget effect on your cross semi-variogram is
        too low, same problem as (a)

        (c) your negative weights are not so large but your
        data is (for example) highly skewed. In this case you
        may get a fairly small negative weight on a very large
        sample value. Your problem here is not negative
        weights but the skewness on your data.

        Hope this helps
        Isobel
        http://uk.geocities.com/drisobelclark

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      • Pierre Goovaerts
        Hi Laure, One of the main culprits for negative cokriging weights is the ordinary cokriging constraint that the sum of the secondary weights must be zero. I
        Message 3 of 5 , Sep 4, 2003
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          Hi Laure,

          One of the main culprits for negative cokriging weights
          is the ordinary cokriging constraint that the sum of the
          secondary weights must be zero. I found that the frequency
          and magnitude of negative cokriging weights greatly decreased
          when using a single constraint that primary and secondary
          data weights must sum to one (referred to as standardized
          cokriging in Gslib software). This issue is discussed in my book
          and in the following publication:

          Goovaerts, P. 1998. Ordinary cokriging revisited.
          Mathematical Geology, 30(1): 21-42.

          Cheers,

          Pierre

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

          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 Thu, 4 Sep 2003 lfontaine@... wrote:

          > Hi Mailinglist!!!
          >
          > I have got some problems with negative weight in my cokriging, they induce
          > negative grade. Have you got some advice or publication to help me.I hope
          > you can help me with some of your answers.
          >
          > Thank
          >
          > Laure
          >
          >
          >
          > Laure FONTAINE
          > Services des Réserves
          > COGEMA BUM/DT
          > tél: 33 1 39 26 32 05
          > Fax: 33 1 39 26 27 31
          >
          >
          >
          > --
          > * To post a message to the list, send it to ai-geostats@...
          > * As a general service to the users, please remember to post a summary of any useful responses to your questions.
          > * To unsubscribe, send an email to majordomo@... with no subject and "unsubscribe ai-geostats" followed by "end" on the next line in the message body. DO NOT SEND Subscribe/Unsubscribe requests to the list
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          >
          >


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        • sebastiano trevisani
          Hi! There is something about negative weights in geostatistics for natural Resources Evaluation of Pierre Goovaerts. Also in Srivastava s Applied
          Message 4 of 5 , Sep 4, 2003
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            Hi!
            There is something about negative weights in "geostatistics for natural
            Resources Evaluation" of Pierre Goovaerts. Also in Srivastava's
            "Applied geostatistics" you can find something of useful.

            Sebastiano





            At 05:29 PM 9/4/2003 +0200, lfontaine@... wrote:
            >Hi Mailinglist!!!
            >
            >I have got some problems with negative weight in my cokriging, they induce
            >negative grade. Have you got some advice or publication to help me.I hope
            >you can help me with some of your answers.
            >
            >Thank
            >
            >Laure
            >
            >
            >
            >Laure FONTAINE
            >Services des Réserves
            >COGEMA BUM/DT
            >tél: 33 1 39 26 32 05
            >Fax: 33 1 39 26 27 31
            >
            >
            >
            >--
            >* To post a message to the list, send it to ai-geostats@...
            >* As a general service to the users, please remember to post a summary of
            >any useful responses to your questions.
            >* To unsubscribe, send an email to majordomo@... with no subject and
            >"unsubscribe ai-geostats" followed by "end" on the next line in the
            >message body. DO NOT SEND Subscribe/Unsubscribe requests to the list
            >* Support to the list is provided at http://www.ai-geostats.org



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          • lfontaine@cogema.fr
            Hi Mailinglist!!! thank you very much for the information ! Laure Laure FONTAINE Services des Réserves COGEMA BUM/DT tél: 33 1 39 26 32 05 Fax: 33 1 39 26 27
            Message 5 of 5 , Sep 5, 2003
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              Hi Mailinglist!!!

              thank you very much for the information !


              Laure

              Laure FONTAINE
              Services des Réserves
              COGEMA BUM/DT
              tél: 33 1 39 26 32 05
              Fax: 33 1 39 26 27 31



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