Hi,
The four variograme models below are fitted to the same dataset. I got
a *warning
message *while cross validating a fitted linear variogram model as


Warning message:In sqrt(ret[[var.name]]) : NaNs produced


from this R script
lin.kcv <- krige.cv(yield ~ 1, canmod.sp, model = lin.var,nmax=100, nfold =
5)

what is the meaning of this warning? Each time I run this R script, I got
different values for the cross validation statistics of linear.

Model         RMSE    MSDR
Spherical      0.66    1.61
Gaussian       0.62    3.17
Exponential    0.65    1.91
Linear         95.91   83.25


These valueslook very strange compared to others because of warning message
above. How do I explain this?
 I made effort to redefine my nfold to be 10 but still give the same
warning.

Thanks
Moshood

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