[R] nls

[Komanduru Sai C]

Hi,

I am using nls library

df <- read.table("data.txt", header=T);						
library(nls);
fm <- nls(y ~ a*(x+d)^(-b), df, start=list(a=max(df->y,na.rm=T)/2,b=1,d=0));
coef(fm); 
q();

When i am using the above routine i am getting the following error

Error in nlsModel(formula, mf, start) : singular gradient matrix at initial 
parameter estimates

Can some one help me in this.

The data.txt file looks like this


x                y                z
1.0                NA                478
2.0                NA                473
3.0                NA                449
4.0                NA                446
5.0                NA                438
6.5                NA                437
6.5                NA                437
8.0                NA                427
9.0                NA                426
10.0                NA                425
11.0                NA                424
14.0                NA                423
14.0                NA                423
14.0                NA                423
14.0                NA                423
14.0                NA                423
.........

The y field has some values at the bottom.

Thanks,
SAi