Hello, I have a question about Simon Wood's gam function. Suppose I have a simple model n<-100 x <- runif(n, 0, 1); y<-x*x data<-data.frame(x,y) ct<-gam(y~ s(x,k = 5)) how could I estimate first derivative of the smooth. From what I understand, i could get coefficients of the fit from ct2<-gam(y~ s(x,k = 5),control =gam.control(absorb.cons = FALSE)) coeff(ct2) to get unconstrained coefficient estimates for the model (this was suggested in response to a similar question in 2005), but how could I get derivative of the basis? Thanks! Roman Torgovitsky Doctoral Student Department of Biostatistics Harvard University