On 08/23/2010 05:45 PM, Kerry Ritter wrote:
Hi. I am using library "gstat" in R. My question is why do I get
different SSErr's when I fit the variogram model using fit.variogram
than when I fix the parameters in fit.variogram using the exact same
parameters obtained from the first fit. My expectation is that these
would be the same. What is SSErr actually calculating?
Thanks,
Kerry
Hi Kerry,
The following example illustrates that fit.variogram is sensitive to the
start parameters you use for Gauss-Newton fitting:
data(meuse)
vgm1 <- variogram(log(zinc)~1, ~x+y, meuse)
v1 = fit.variogram(vgm1, vgm(1,"Sph",300,1))
# Use fit above as initial guess
v2 = fit.variogram(vgm1, v1)
v1
# model psill range
#1 Nug 0.0506555 0.0000
#2 Sph 0.5906009 896.9702
v2
# model psill range
# 1 Nug 0.05066039 0.000
# 2 Sph 0.59060578 897.006
So the difference in SSerr is caused by a different fit by
fit.variogram, which in turn is caused by a different initial variogram
model guess.
regards,
Paul
--
Drs. Paul Hiemstra
Department of Physical Geography
Faculty of Geosciences
University of Utrecht
Heidelberglaan 2
P.O. Box 80.115
3508 TC Utrecht
Phone: +3130 253 5773
http://intamap.geo.uu.nl/~paul
http://nl.linkedin.com/pub/paul-hiemstra/20/30b/770
_______________________________________________
R-sig-Geo mailing list
R-sig-Geo@stat.math.ethz.ch
https://stat.ethz.ch/mailman/listinfo/r-sig-geo
