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.
