Thank you Berwin. Ok, I take your point. I normally do nls modelling interactively but this time I was given a set of data so I tried to use an approach which I use quite often in lm or in plotting to pdf file. I obviously was not successful and there is nothing about it in documentation or at least I did not find it :-).
I used Katharine's solution and will look on Gabor's too later. Regards Petr Berwin A Turlach <[EMAIL PROTECTED]> napsal dne 26.06.2008 20:59:20: > G'day Petr, > > On Thu, 26 Jun 2008 13:57:39 +0200 > Petr PIKAL <[EMAIL PROTECTED]> wrote: > > > I just encountered a strange problem with nls formula. I tried to use > > nls in cycle but I was not successful. I traced the problem to some > > parse command. > > > > [...] > > > > > > I am not sure if this behaviour is a bug or feature. [...] > > It is definitely a feature. > > It is an error to believe that all modelling functions that use > modelling formulae use the same syntax for their modelling formulae. > This is, perhaps, easiest realised by observing how lm() and nls() > interpret "*" and "/" in model formulae. > > In nls(), "[..]" can be used to index parameters, if the parameter is > allowed to change between groups in the data. This seems to be a > little known feature, though there is an example that uses that feature > in MASS. The contributed documentation "An Introduction to R: Software > for Statistical Modelling & Computing" by Petra Kuhnert and Bill > Venables, available from CRAN, also has such an example on pages 134 > and 230. > > The fact that nls() allows you to use "[..]" to index parameters in the > model formulae seems to conflict with the way you wanted to specify > the observed values in the formula. I guess Gabor's solution is a fix > for your problem. > > Cheers, > > Berwin > > =========================== Full address ============================= > Berwin A Turlach Tel.: +65 6515 4416 (secr) > Dept of Statistics and Applied Probability +65 6515 6650 (self) > Faculty of Science FAX : +65 6872 3919 > National University of Singapore > 6 Science Drive 2, Blk S16, Level 7 e-mail: [EMAIL PROTECTED] > Singapore 117546 http://www.stat.nus.edu.sg/~statba ______________________________________________ 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.
