Hi, I have a data with three variables (X,Y,Z) and I have an equation as Z=X/(1+L*X/Y) where L is a constant which need to be estimated from data. How should I write the formula in lm or is it possible to fit a linear model in this case? Thanks! Hallen [[alternative HTML version deleted]]
On 19.02.2013 11:23, hellen wrote:> Hi, > I have a data with three variables (X,Y,Z) and I have an equation as > Z=X/(1+L*X/Y) where L is a constant which need to be estimated from data. > How should I write the formula in lm or is it possible to fit a linear > model in this case?Neither, it is nonlinear in the parameters. See ?nls or ?optim, for example. Uwe Ligges> > Thanks! > Hallen > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help at 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. >
Uwe Ligges <ligges <at> statistik.tu-dortmund.de> writes:> > On 19.02.2013 11:23, hellen wrote: > > Hi, > > I have a data with three variables (X,Y,Z) and I have an equation as > > Z=X/(1+L*X/Y) where L is a constant which need to be estimated from data. > > How should I write the formula in lm or is it possible to fit a linear > > model in this case? > > Neither, it is nonlinear in the parameters. See ?nls or ?optim, for example.Well, if the Z values are not too small, you can linearize it as U = (X Y - Y Z) / Z = L X and solve it with lm(U ~ X - 1), that is without absolute term.> Uwe Ligges > > > > > Thanks! > > Hallen > > >