Hi r-help-boun...@r-project.org napsal dne 24.02.2009 12:41:50:
> > Hi Peter, > > You are totally right and it was a miscalculating and misunderstanding from > me. > Regarding the R-squared calculation of non linear model (question 2), is > there any way to do that? I am not an expert statistician, Douglas Bates is so see his answer to similar question few years ago http://tolstoy.newcastle.edu.au/R/help/02b/0482.html Regards Petr > > Regards > Saeed > > Petr Pikal wrote: > > > > Hi > > > > r-help-boun...@r-project.org napsal dne 24.02.2009 11:31:22: > > > >> > >> Hi, > >> > >> Thank you for the reply and suggestions. > >> > >> I have two questions? > >> 1) If I want to use log, it seems that I have to take log from both > > sides of > >> the model which will lead to lm(log(q)~log(-depth)). What is > > tehdifference > >> between this syntax and lm(log(q) ~ I(-depth))? > > > > > > If you have > > > > y = a*exp(-b*x) then log of this equation is > > > > log(y) = log(a) - b * x > > > > at least I was told that by my teacher back at school some decades ago > > that log(exp(x)) = x. > > > > You can prove it by > > > > log(exp(whatever)) > > > > interactively in R > > > > Regards > > Petr > > > >> > >> 2) How can I calculate the R-squared of a fitted non linear model? > >> > >> Regards > >> Saeed > >> > >> > >> Christian Ritz-3 wrote: > >> > > >> > Hi Saeed, > >> > > >> > one approach is to try out several initial value combinations for a > > and b. > >> > > >> > It often helps to find initial values of the same order of magnitude > > and > >> > of the same sign > >> > as the final estimates. > >> > > >> > To get such initial values, you could linearize the model: > >> > > >> > lm(log(q) ~ I(-depth)) > >> > > >> > > >> > and supply the estimated coefficients from the linear regression as > >> > starting values: > >> > > >> > nreg <- nls(q ~ a*exp(-b*depth), start = list(a = 0.76168, b = > > -0.08484)) > >> > summary(nreg) > >> > > >> > > >> > 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. > >> > > >> > > >> > >> -- > >> View this message in context: > > http://www.nabble.com/An-error-in-fitting-a-non- > >> linear-regression-tp22118160p22179525.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. > > > > > > -- > View this message in context: http://www.nabble.com/An-error-in-fitting-a-non- > linear-regression-tp22118160p22180225.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.