Hi I have a data set with two variables "q" and "depth" as follows:
q<-c(tapply(weight[Soil=="Jy"], Depth[Soil=="Jy"], mean)). This commns returns 7 "q" values: 0.687900000 0.845550000 0.405416667 0.152766667 0.033100000 0.031400000 0.005183333 The "depth" values are produced using this command whish "depth" shows teh soil depth: depth <--c(5,15,25,35,45,55,65). This return these values for "depth": [1] -5 -15 -25 -35 -45 -55 -65 I have uploaded the plot file in below: http://www.nabble.com/file/p22118160/plot.doc plot.doc Now I want to fit the following decaying exponential model to our data presented in the plot file such that depth is X and q is Y. nreg<-nls(q~a*exp(-b*depth), start=list(a=1, b=0.5)). This command returns the following error: Error in nls(q ~ a * exp(-b * depth), start = list(a = 1, b = 0.5)) : singular gradient However, if I use positive values of depth i.e. [1] 5 15 25 35 45 55 65 then I recieve the following error: Error in numericDeriv(form[[3]], names(ind), env) : Missing value or an infinity produced when evaluating the model Notice that though in the plot depth is drawn on Y axis but in the regression model "depth" in independent. Plot shows the real world of what happne to the crop root growth. Thank you. Saeed Ahmadi -- View this message in context: http://www.nabble.com/An-error-in-fitting-a-non-linear-regression-tp22118160p22118160.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ 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.