Dear all I have troubles with correct evaluating/structure of nls input x<-1:10 y<-1/(.5-x)+rnorm(10)/100 form <- structure(list(a = list(quote(y ~ 1/(a - x)), "list(a=mean(y))")), .Names = "a") This gives me an error due to not suitable default starting value fit <- nls(form [[1]] [[1]], data.frame(x=x, y=y)) This works and gives me a result fit <- nls(form [[1]] [[1]], data.frame(x=x, y=y), start=list(a=mean(y))) How to organise list "form" and call to nls to enable to use other then default starting values. I thought about something like fit <- nls(form [[1]] [[1]], data.frame(x=x, y=y), start=get(form [[1]] [[2]])) but this gives me an error so it is bad function. (BTW I tried eval, assign, sustitute, evalq and maybe some other options but did not get it right. I know I can put starting values interactively but what if I want them computed by some easy way which is specified by second part of a list, like in above example. If it matters WXP, R2.9.0 devel. Regards Petr