Martin Maechler <[EMAIL PROTECTED]> writes: > >>>>> "KKWa" == Ko-Kang Kevin Wang <[EMAIL PROTECTED]> > >>>>> on Thu, 10 Jul 2003 23:00:00 +1200 (NZST) writes: > > KKWa> Try: ?lm > > no. see below > > KKWa> On 10 Jul 2003, Gorazd Brumen wrote: > > >> Date: 10 Jul 2003 12:54:46 +0200 From: Gorazd Brumen > >> <[EMAIL PROTECTED]> To: [EMAIL PROTECTED] > >> Subject: [R] Simple linear regression > >> > >> Dear all, > >> > >> My friend wants to fit a model of the type > >> > >> z = a x^n y^m + b, > >> > >> where x, y, z are data and a, b, n, m are unknown > >> parameters. > >> > >> How can he transform this to fit in the linear regression > >> framework? Any help would be appreciated. > > He can't. When all 4 a, b, n, m are parameters, this is a > non-linear regression problem. --> Function nls() > > Now, effectively 2 of the 4 are linear, 2 are non linear; > such a problem is denoted as `` partially linear least-squares '' > In such a case it's quite important (for efficiency and > inference reasons) to make use of this fact. > > ---> use nls(...., method = "plinear" , ....)
I think it should be 'algorithm = "plinear"' The full call would be something like nls(z ~ cbind(x^n*y^m, 1), data = mydata, start=c(n = 1.0, m = 2.0), algorithm = "plinear") Must the exponents n and m be positive? If so, I recommend using the logarithm of the exponents as the parameters in the optimization nls(z ~ cbind(x^exp(logn)*y^exp(logm), 1), data = mydata, start=c(logn = 0., logm = log(2.0)), algorithm = "plinear") ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help