[R] nlme Fixed Variance Function

[Agostino Moro]

Dear R users,

I am trying to fit a gls model and weight my data points using a
VarFixed structure. I have found many examples, but I do not
understand the difference between the following models with varFixed
specified in a different way:

mod<-gls(y~x,weights=varFixed(~1/invsigma)

mod<-gls(y~x,weights=varFixed(~invsigma)

In my case I would simply like to weigh my data points by their
inverse variance.

Any help would be greatly appreciated!

Cheers,

Agostino