[R] nonlinear fitting when both x and y having measurement e

Etsushi Kato ekato at ees.hokudai.ac.jp
Wed Sep 12 14:42:58 CEST 2001

Thank you very much Prof. Ripley and Martyn Plummer.
Also I got one suggestion of using ORDPACK at http://www.netlib.org/.

> > That is not a least-squares problem.  Even in the simple linear case (one
> > x one y) it's a hard problem, one that cannot be solved without more
> > information (for example on the ratio of the error variances, or knowing
> > one of them). As far as I know there is no software available in R for
> > that case (although it's not hard to write).

My data is allometric relationship of biological data, and perhaps it is
OK to assume both variables having equal accuracies.  So I was just
considering using orthogonal distance to the nonlinear curve.

> > I think you need to write down a suitable likelihood and optimize it
> > numerically (with optim).

It's a bit difficult for me to construct likelihood function, because
right now there is no books you suggested around me...
For the moment, I'm considering using ORDPACK.  I'll try to construct
R code later.

Best Regards,
Etsushi Kato
ekato at ees.hokudai.ac.jp
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