Hi Kate and Fernando, I'm late into this thread, but from reading it I get the impression that Fernando really wants to do *robust* (as opposed to least-squares) non-linear model fitting. His proposal to set residuals to zero when they are outside a given bound is a very special case of an M-estimator, namely (if I'm not mistaken) the so-called "Huber skipped-mean", an M-estimator with psi-function psi <- function(x, k) ifelse(abs(x) <= k, x, 0) It is known that this can be far from optimal, and either using Huber-psi or "a redescender" such as Tukey's biweight can be considerably better. Also note that the standard inference (std.errors, P-values, ...) that you'd get from summary(nlsfit) or anova(nls1, nl2) is *invalid* here, since you are effectively using *random* weighting.
The nlrob() function in package 'robustbase' implements M-estimation of nonlinear models directly. Unfortunately, how to do correct inference in this situation is a hard problem, probably even an open research question in parts. I would expect that "the" bootstrap should work if you only have a few outliers. I don't have time at the moment to look at the example data and the model, and show you how to use it for nlrob(); if you find a way to you it for nls() , then the same should work for nlrob(). I'm CCing this to the specialists for "Robust Stats with R" mailing list, R-SIG-robust. Best regards, Martin Maechler ETH Zurich >>>>> "KateM" == Katharine Mullen <[EMAIL PROTECTED]> >>>>> on Fri, 9 May 2008 15:50:08 +0200 (CEST) writes: KateM> You can take minpack.lm_1.1-0 (source code and MS Windows build, KateM> respectively) from here: KateM> http://www.nat.vu.nl/~kate/minpack.lm_1.1-0.tar.gz KateM> http://www.nat.vu.nl/~kate/minpack.lm_1.1-0.zip KateM> The bug that occurs when nprint = 0 is fixed. Also fixed is another KateM> problem suggested your example: when the argument par is a list, calling KateM> summary on the output of nls.lm was not working. KateM> I'll submit the new version to CRAN soon. KateM> This disscusion has been fruitful - thanks for it. KateM> On Fri, 9 May 2008, Katharine Mullen wrote: >> You indeed found a bug. I can reproduce it (which I should have tried to >> do on other examples in the first place!). Thanks for finding it. >> >> It will be fixed in version 1.1-0 which I will submit to CRAN soon. >> >> On Fri, 9 May 2008, elnano wrote: >> >> > >> > Find the data (data_nls.lm_moyano.txt) here: >> > ftp://ftp.bgc-jena.mpg.de/pub/outgoing/fmoyano >> > >> > >> > >> > Katharine Mullen wrote: >> > > >> > > Thanks for the details - it sounds like a bug. You can either send me the >> > > data in an email off-list or make it available on-line somewhere, so that >> > > I and other people can download it. >> > > >> > > >> > > ______________________________________________ >> > > 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. >> > > >> > > >> > >> > -- >> > View this message in context: http://www.nabble.com/function-in-nls-argument-tp17108100p17146812.html >> > Sent from the R help mailing list archive at Nabble.com. >> > >> > ______________________________________________ >> > 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. >> > >> >> ______________________________________________ >> 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. >> KateM> ______________________________________________ KateM> R-help@r-project.org mailing list KateM> https://stat.ethz.ch/mailman/listinfo/r-help KateM> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html KateM> and provide commented, minimal, self-contained, reproducible code. ______________________________________________ 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.