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?
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.
