Dear Pierre,
I must apologise. I totally misread your command file. So please ignore my
previous comment!
Gerard.
>Date: Thu, 24 May 2001 14:57:33 +0200
>To: "Gagnon,Pierre [Montreal]" <[EMAIL PROTECTED]>
>From: Gerard Heuvelink <[EMAIL PROTECTED]>
>Subject: Re: Sequential gaussian simulation
>Cc: [EMAIL PROTECTED]
>
>Dear Pierre,
>
>It looks as if your covariance matrix is not positive-definite. The sill
>of the cross-variogram should not exceed the square root of the products
>of the sills of the variograms (i.e., 0.35 should not exceed
>sqrt(0.2*0.5)). Violating this condition may cause very strange results.
>
>Gerard
>
>
>At 05:59 PM 5/23/2001 -0400, you wrote:
>>Hi all,
>>
>>I am trying to simulate a locally gaussian field using gstat. The command
>>file looks like this:
>>
>>#
>># Strates: 0=Sud 1=Nord 2=Voie navigable
>>#
>>data(HG0): 'Hg89Export.txt', x=4, y=3, v=5, log, max=12, min=3, radius=3000,
>>b=[0] ;
>>data(HG1): 'Hg89Export.txt', x=4, y=3, v=5, log, max=12, min=3, radius=3000,
>>b=[0] ;
>>data(HG2): 'Hg89Export.txt', x=4, y=3, v=5, log, max=12, min=3, radius=3000,
>>b=[0] ;
>>data(): 'GrilleLSF.txt', x=1, y=2, s=3 ;
>>variogram(HG0): .2 Exp(3266) ;
>>variogram(HG1): .5 Exp(3266) ;
>>variogram(HG2): .35 Exp(3266) ;
>>method: gs;
>>set output='pr89sim.out';
>>set nsim=50;
>>
>>The prediction file contains 1531 positions located on a square grid
>>covering a lake divided in three strata (North shore, South shore and center
>>channel). The output has the following strange characteristic: The
>>variability of predicted values at a given prediction location depends on
>>its order in the file. In the original GrilleLSF.txt file, the prediction
>>locations go from west to east, south to north. The standard deviation of
>>predicted values, depicted here as the size of the circles, looks like this:
>>
>>Notice the sudden increase in variability around x=544000 which, given the
>>conditioning data, is rather unexpected. When the order of the file is
>>reversed, everything else kept the same, the variability of simulated values
>>becomes :
>>
>>Now the most variable section is in the west, up to x=551000. It is as if
>>the first, maybe 500, points in the data() file were not treated the same as
>>the rest. What might cause this?
>>
>>I hope the figures make it througt the list server.
>>
>>Thanks in advance.
>>
>>Pierre Gagnon
>>Centre Saint-Laurent
>>105 McGill, Montréal
>>(Québec) H2Y 2E7
>>514 496 1456
>>http://www.qc.ec.gc.ca/csl/ <http://www.qc.ec.gc.ca/csl/>
>>
>
>Gerard B.M. Heuvelink
>Institute for Biodiversity and Ecosystem Dynamics
>Science Faculty
>Universiteit van Amsterdam
>Nieuwe Achtergracht 166
>1018 WV Amsterdam
>The Netherlands
>
>tel +31 20 5257448 (secretary +31 20 5257451)
>fax +31 20 5257431
>email [EMAIL PROTECTED]
>http://www.frw.uva.nl/soil/Welcome.html
Gerard B.M. Heuvelink
Institute for Biodiversity and Ecosystem Dynamics
Science Faculty
Universiteit van Amsterdam
Nieuwe Achtergracht 166
1018 WV Amsterdam
The Netherlands
tel +31 20 5257448 (secretary +31 20 5257451)
fax +31 20 5257431
email [EMAIL PROTECTED]
http://www.frw.uva.nl/soil/Welcome.html
