Hi
The problem is quite simple and is not a problem of numerical instability.
The problem is that when I use o power model
(reducing to a linear model when the exponent is 1)
both vmodel.exe (the code that generates
variogram model values) as well as Kt3d.exe
don't reproduce the nugget effect that I have imposed.
So, the problem seems related to the way in which
Gslib build the variogram models.
Well, I'll give a look to the code....maybe I'll see what is going on....
Sebastiano
At 14.31 29/05/2007, Adrián Martínez Vargas wrote:
I really don know why you have problems with the
model. It is valid for kriging but it is not
valid for Sequential Gaussian
Simulation.<?xml:namespace prefix = o ns =
"urn:schemas-microsoft-com:office:office" />
The problems with kt3d, if you pretend to do
kriging with trend or drift, can be related to
the shape of the data and drift. If data
position is linear combination of the drif the
kriging system dont have trivial solution. In
the case of linear drift the estimation can be
unstable if data position is close to a strike line!
Notice that if you are using <?xml:namespace
prefix = st1 ns =
"urn:schemas-microsoft-com:office:smarttags" />
UK you have to get the variogram of residuals!
It can be suspicious in some cases, then it is
preferable to use IRF-K approach.
Dr. Adrian Martínez Vargas
Departamento de Geología
ISMM, Las Coloradas s/n
Moa, Holguín
Cuba
CP 83329
-----Original Message-----
From: sebastiano trevisani <[EMAIL PROTECTED]>
To: ai-geostats@jrc.it
Date: Mon, 28 May 2007 13:04:01 +0200
Subject: AI-GEOSTATS: nugget effect plus linear model Gslib
> Dear list member
>
> I was working with gslib library and I had some troubles in trying to
> interpolate with a linear variogram
> (well, a power model with exponent = 1) and a nugget effect. In
> particular both vmodel.exe as well as kt3d.exe don't
> care about the value of the nugget effect imposed.
> So I'm wondering If anyone has experienced something similar.
> Then, I have another question: have you any idea in which I can change
> gslib
> code in order to perform factorial kriging?
> Sebastiano T.
>
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