Dear I investigated herbicide affect on weeds growth (dose-response). I used drc package and fitted data to best model by mselect function and parameters of models. For some data, Logistic model was the best and for others, Weibull. But when I wanted to draw relative potency curve, the R-program displayed error massage just for Weibull model (attachment files). could you please help me? thanks a lot. your sincerely, Ahmad Rahbari -------------- next part -------------- An embedded and charset-unspecified text was scrubbed... Name: error.txt URL: <https://stat.ethz.ch/pipermail/r-help/attachments/20191023/3290c289/attachment.txt>