R version 2.7.0 (2008-04-22)
Copyright (C) 2008 The R Foundation for Statistical Computing
ISBN 3-900051-07-0

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> library(gstat)
Loading required package: sp
> data(meuse)
> v=variogram(log(zinc)~1,~x+y,meuse,cutoff=500,wi=100)
> v$gamma=c(0.5,1,2,3,3)
> fit.variogram(v, vgm(1, "Sph", 300, 0),warn.if.neg=TRUE)
  model    psill    range
1   Nug 0.000000    0.000
2   Sph 7.878087 1567.749
Warning message:
In fit.variogram(v, vgm(1, "Sph", 300, 0), warn.if.neg = TRUE) :
  partial sill or nugget fixed at zero value
> fit.variogram(v, vgm(1, "Sph", 300, 0),warn.if.neg=FALSE)
  model    psill    range
1   Nug 0.000000    0.000
2   Sph 7.878087 1567.749
>