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.