nugget in variogram

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Hello everybody
I am new on geostatistics so maybe my question is trivial or is
already answered (I can not find the solution in the thread list). I
have a variogram where I did not fix the nugget, because doing it
was giving "singular models". I would like to know the nugget ratio
of my variograms but I don't know how to get then the nugget value.
So I did look in the output of variogram and did take the minimum
value of gamma. Is this correct?
Well, it's not the usual way, where you would fit a model:

library(gstat)
data(meuse)
coordinates(meuse) = ~x+y
v = variogram(log(zinc)~1, meuse)
v.m = fit.variogram(v, vgm(1, "Sph", 500, 1))
v[1, "gamma"] # your estimator:
plot(v, v.m)
v.m$psill[1] / sum(v.m$psill) # the usual estimator:

Only when you have plenty of measurements at very short distances
apart, I can imagine you would use the sample variogram (v) value.
Thanks very much for your attention. 

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Edzer Pebesma
Institute for Geoinformatics (ifgi), University of M?nster
Weseler Stra?e 253, 48151 M?nster, Germany. Phone: +49 251
8333081, Fax: +49 251 8339763  http://ifgi.uni-muenster.de
http://www.52north.org/geostatistics      e.pebesma at wwu.de
Sorry, this was too fast again:

v[1,"gamma"]
# or
v.m$psill[1]

are estimators of the nugget variance;

v.m$psill[1] / sum(v.m$psill)

is an estimator of the nugget-to-sill ratio.

On 09/30/2010 04:13 PM, Arantzazu Blanco Bernardeau wrote:
Hello everybody
I am new on geostatistics so maybe my question is trivial or is
already answered (I can not find the solution in the thread list). I
have a variogram where I did not fix the nugget, because doing it
was giving "singular models". I would like to know the nugget ratio
of my variograms but I don't know how to get then the nugget value.
So I did look in the output of variogram and did take the minimum
value of gamma. Is this correct?
Well, it's not the usual way, where you would fit a model:

library(gstat)
data(meuse)
coordinates(meuse) = ~x+y
v = variogram(log(zinc)~1, meuse)
v.m = fit.variogram(v, vgm(1, "Sph", 500, 1))
v[1, "gamma"] # your estimator:
plot(v, v.m)
v.m$psill[1] / sum(v.m$psill) # the usual estimator:

Only when you have plenty of measurements at very short distances
apart, I can imagine you would use the sample variogram (v) value.

Thanks very much for your attention. 

	[[alternative HTML version deleted]]

_______________________________________________
R-sig-Geo mailing list
R-sig-Geo at stat.math.ethz.ch
https://stat.ethz.ch/mailman/listinfo/r-sig-geo

Edzer Pebesma
Institute for Geoinformatics (ifgi), University of M?nster
Weseler Stra?e 253, 48151 M?nster, Germany. Phone: +49 251
8333081, Fax: +49 251 8339763  http://ifgi.uni-muenster.de
http://www.52north.org/geostatistics      e.pebesma at wwu.de