Hi r-help-boun...@r-project.org napsal dne 20.02.2009 11:21:26:
> > 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 With b=0.05 it will converge, however the model seems to be wrong. depth <--c(5,15,25,35,45,55,65) y<-c(0.687900000, 0.845550000, 0.405416667, 0.152766667, 0.033100000, 0.031400000,0.005183333) plot(depth,y) nreg<-nls(y~a*exp(-b*depth), start=list(a=1, b=0.05)) lines(depth, predict(nreg)) Regards Petr > > 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. ______________________________________________ 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.
