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