Hi Dear doctor Myers
Thank you for replying
I have constructed a more general variogram model, in
which all of the parameters are varying with
direction. My model more general than range anisotropy
and sill anisotropy. Since I want to simulate from
this model ,with cholesky decomposition method, I need
the covariogram model, which is respected to my
variogram model. Therefore I need the relation between
variogram and covariogram. In fact I need to specify
C(0) in term of the parameters of my model ( My model
has 6 parameters c01,c02( Nuggets) ,c1,c2 (partial
sill) and a1,a2 (Ranges) ), because when it be known
C(h) = C(0) - g(h)
Thank you again: Webster
--- "Donald E. Myers" <[EMAIL PROTECTED]> wrote:
> Two observations
>
> 1. The relationship between the variogram and the
> covariance function is
> only valid in the case of second order stationarity
> (presumably you are
> making the assumption of second order stationarity)
>
> 2. You said you had an "Anisotropic variogram", do
> you mean you have a
> model for a variogram with anisotropy or do you mean
> that the
> directional sample variograms indicate a change in
> the sill with
> direction? The apparent sill indicated by a sample
> variogram
> (directional or not) will combine the nugget effect
> component and also
> the sill due to the non-nugget part of the variogram
> model, in addition
> the nugget effect component will be separately
> evident on the graph of
> the sample variogram. If you check the various
> geostatistical software
> packages you will see that they only allow for a
> geometric anisotropy in
> the variogram model, this means that the RANGE of
> the variogram changes
> with respect to direction, the software does not
> allow the sill to
> change with respect to direction. To allow the sill
> to change you would
> need a "zonal" aniostropy, i.e., a non-geometric
> anisotropy and the
> problem is constructing a valid variogram model with
> this kind of
> anisotropy.
>
> A. Journel and I showed that one method that had
> been used leads to
> semi-definite models, i.e., non-invertible
> coefficient matrices for the
> * kriging system 1990, D .E. Myers and A. Journel,
> Variograms with Zonal
> Anisotropies and Non-Invertible Kriging Systems.
> Math. Geology 22, 779-785
>
>
>
> Donald E. Myers
> http://www.u.arizona.edu/~donaldm
>
> jack webster wrote:
>
> >Hi all list members
> >Suppose that g denote the semi-variogram and C
> >denote the Covariogram functions. According to
> >Cressie(1993, P. 67) the relation is
> > g(h) = C(0) - C(h)
> >where h is the distance vector.In the isotropic
> case
> > C(0) = total sill = c0 +
> c
> >I have an Anisotropic Variogram in which c is
> varying
> >with direction.Therefore my question is what is
> C(0)
> >in this case?
> >
> >=====
> >
> >
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