Write out the objective functions that they are minimizing and it will be clear they are different so you can't expect the same results.
On Wed, Mar 5, 2008 at 8:53 AM, Wolfgang Waser <[EMAIL PROTECTED]> wrote: > Dear all, > > I did a non-linear least square model fit > > y ~ a * x^b > > (a) > nls(y ~ a * x^b, start=list(a=1,b=1)) > > to obtain the coefficients a & b. > > I did the same with the linearized formula, including a linear model > > log(y) ~ log(a) + b * log(x) > > (b) > nls(log10(y) ~ log10(a) + b*log10(x), start=list(a=1,b=1)) > (c) > lm(log10(y) ~ log10(x)) > > I expected coefficient b to be identical for all three cases. Hoever, using my > dataset, coefficient b was: > (a) 0.912 > (b) 0.9794 > (c) 0.9794 > > Coefficient a also varied between option (a) and (b), 107.2 and 94.7, > respectively. > > Is this supposed to happen? Which is the correct coefficient b? > > > Regards, > > Wolfgang > > -- > Laboratory of Animal Physiology > Department of Biology > University of Turku > FIN-20014 Turku > Finland > > ______________________________________________ > 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.
