Dear Aleksi, there are other approaches you could consider: using nls or gnls (in the package nlme):
m1 <- nls(y ~ a[group]*x^b[group], start=list(a=c(1, ..., 1), b=c(1, ..., 1))) or m2 <- gnls(rate ~ a*x^b, params=list(a~group-1, b~group-1), start=list(a=c(1, ..., 1), b=c(1, ..., 1))) In both cases there should be specified as many initial values of a and b as there are groups (levels in the factor group). Both approaches can also be used to specified simplified models where some parameter is assumed to be in common for all groups. Christian ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
