# Re: [R] nls

From: Spencer Graves <spencer.graves_at_pdf.com>
Date: Sat 23 Sep 2006 - 07:52:30 GMT

I used "debug" to walk through your example line by line, I found that the error message was misleading. By making as.vector(semivariance) and as.vector(h) columns of a data.frame, I got it to work. My revised code appears below.

Thanks for providing a self-contained and relatively simple example. Without it, I could have done little more that suggest 'traceback' (which provided zero information when I tried it) and 'debug'.

```      Hope this helps.
Spencer Graves

```

fit.gaus<-function(coordinates,values,guess.c0,guess.c1,guess.a) {

```         long<-rep(coordinates[,1],each=length(coordinates[,1]))

lag.long<-t(matrix(long,nrow=length(coordinates[,1]),byrow=TRUE))
dif.long <-(lag.long-t(lag.long))^2
lat <-rep(coordinates[,2],each=length(coordinates[,2]))
lag.lat<-t(matrix(lat,nrow=length(coordinates[,2]),byrow=TRUE))
dif.lat <-(lag.lat-t(lag.lat))^2
h <-sqrt(dif.long+dif.lat)

if( length(values[1,])>1)
{
y.m <-apply(values,1,sum,na.rm=TRUE)
y.m <-as.matrix(y.m)
y.mod <-(1/length(values[1,]))*(y.m)
}
else
{
y.mod <-as.matrix(values)
}

semi <-rep(y.mod,each=length(y.mod))
mat1<-t(matrix(semi,nrow=length(y.mod),byrow=TRUE))
mat2<-t(mat1)
semivariance <-(1/2)*(mat1-mat2)^2

#        model <-semivariance ~c0+c1*(1-exp(-(h^2)/a^2))

DF <- data.frame(smvar=as.vector(semivariance),
h.=as.vector(h) )
mdl <- smvar~c0+c1*(1-exp(-(h.^2)/a^2))

#        parameters <-nls(model,start =

#list(c0=guess.c0,c1=guess.c1,a=guess.a),trace=TRUE)
parameters <-nls(mdl,start =
list(c0=guess.c0,c1=guess.c1,a=guess.a),trace=TRUE,
data=DF )
results <-summary(parameters)
print(results)
```

}

################################

mzabalazo ngwenya wrote:

```> Hello everyone !
>
> I am trying to write a short program to estimate  semivariogram
> parameters. But I keep running into a problem when using the nls
> function.
>
> Could you please shed some light. I have put a sample of one of the
> codes and ran a short example so you see what I mean.
>
> -----------------
>
>
>
> fit.gaus<-function(coordinates,values,guess.c0,guess.c1,guess.a)
> {
>          long<-rep(coordinates[,1],each=length(coordinates[,1]))
>
> lag.long<-t(matrix(long,nrow=length(coordinates[,1]),byrow=TRUE))
>          dif.long <-(lag.long-t(lag.long))^2
>          lat <-rep(coordinates[,2],each=length(coordinates[,2]))
>          lag.lat<-t(matrix(lat,nrow=length(coordinates[,2]),byrow=TRUE))
>          dif.lat <-(lag.lat-t(lag.lat))^2
>          h <-sqrt(dif.long+dif.lat)
>
>
>          if( length(values[1,])>1)
>                {
>                      y.m <-apply(values,1,sum,na.rm=TRUE)
>                      y.m <-as.matrix(y.m)
>                      y.mod <-(1/length(values[1,]))*(y.m)
>             }
>          else
>                {
>                       y.mod <-as.matrix(values)
>             }
>
>         semi <-rep(y.mod,each=length(y.mod))
>         mat1<-t(matrix(semi,nrow=length(y.mod),byrow=TRUE))
>         mat2<-t(mat1)
>         semivariance <-(1/2)*(mat1-mat2)^2
>
>         model <-semivariance ~c0+c1*(1-exp(-(h^2)/a^2))
>         parameters <-nls(model,start =
> list(c0=guess.c0,c1=guess.c1,a=guess.a),trace=TRUE)
>         results <-summary(parameters)
>                       print(results)
> }
> --------------------------
>
>
>>  don <-matrix(c(2,3,9,6,5,2,7,9,5,3),5,2)
>> don
>>
>      [,1] [,2]
> [1,]    2    2
> [2,]    3    7
> [3,]    9    9
> [4,]    6    5
> [5,]    5    3
>
>>  data <-matrix(c(3,4,2,4,6))
>> data
>>
>      [,1]
> [1,]    3
> [2,]    4
> [3,]    2
> [4,]    4
> [5,]    6
>
>> fit.gaus(don,data,2,3,5)
>>
>          [,1]     [,2]     [,3]     [,4]     [,5]
> [1,] 0.000000 5.099020 9.899495 5.000000 3.162278
> [2,] 5.099020 0.000000 6.324555 3.605551 4.472136
> [3,] 9.899495 6.324555 0.000000 5.000000 7.211103
> [4,] 5.000000 3.605551 5.000000 0.000000 2.236068
> [5,] 3.162278 4.472136 7.211103 2.236068 0.000000
> 178.9113 :  2 3 5
> Error in qr.qty(QR, resid) : 'qr' and 'y' must have the same number of
> rows
>
>
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