Julian Burgos jmburgos at u.washington.edu
Thu Nov 8 18:51:05 CET 2007

```Hi Azadeh,

As the warning message is telling you, it seems that your initial
parameters for the covariance functions are not very good.  Something
that you can do is to use the eyefit() function (package geoR) to fit
covariance parameter values (or to test if the values you are using do
generate a variogram curve that is close to your data).  Then you can
use these parameters values as initial values in the variofit() function.

Julian

> I have thise problem in work with the function variofit and nls and dont know how to solve it.
> var1<-variog(data,option="bin")
> var2<-variog(data,option="cloud")
> v1<-var1\$v
> u1<-var1^u
> v2<-var2\$v
> u2<-var2\$u
>   variofit(var1,ini.cov.pars=c(0.005,1.5),cov.model="power",fix.nugget=F,weight="equal")
> variofit: weights used: equal
> variofit: minimisation function used: optim
> Error in if (loss > (.Machine\$double.xmax^0.5) | loss == Inf | loss ==  :
>         missing value where TRUE/FALSE needed
> unreasonable initial value for sigmasq + nugget (too low) in: variofit(var1, ini.cov.pars = c(0.005, 1.5), cov.model = "power",
> .......................................................................................................................
> variofit(var2,ini.cov.pars=c(0.005,1.5),cov.model="power",fix.nugget=F,weight="equal")
> variofit: weights used: equal
> warning: minimisation function nls can not be used with given cov.model.
>           changing for "optim".
> variofit: minimisation function used: optim
> Error in if (loss > (.Machine\$double.xmax^0.5) | loss == Inf | loss ==  :
>   missing value where TRUE/FALSE needed
> In variofit(var2, ini.cov.pars = c(0.005, 1.5), cov.model = "power",  :
>   unreasonable initial value for sigmasq + nugget (too low)
> ...............................................................................................................................
>  nls(v2~c0+ce*(1-exp(-(u2^2)/(ae^2))),start=list(c0=0,ae=30000,ce=20000))
> Error in nls(v2 ~ c0 + ce * (1 - exp(-(u2^2)/(ae^2))), start = list(c0 = 0,  :
>   number of iterations exceeded maximum of 50
>   best regards.
>
>
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