Sorry, its algorithm="brute-force" On Tue, Mar 30, 2010 at 10:29 AM, Corrado <ct...@york.ac.uk> wrote: > Hi Gabor, > > same problem even using nls2 with method=brute-force to calculate the > initial parameters. > > Best, > > Gabor Grothendieck wrote: >> >> You could try method="brute-force" in the nls2 package to find starting >> values. >> >> On Tue, Mar 30, 2010 at 7:03 AM, Corrado <ct...@york.ac.uk> wrote: >> >>> >>> I am using nls to fit a non linear function to some data. >>> >>> The non linear function is: >>> >>> y= 1- exp(-(k0+k1*p1+ .... + kn*pn)) >>> >>> I have chosen algorithm "port", with lower boundary is 0 for all of the >>> ki >>> parameters, and I have tried many start values for the parameters ki >>> (including generating them at random). >>> >>> If I fit the non linear function to the same data using an external >>> algorithm, it fits perfectly and finds the parameters. >>> >>> As soon as I come to my R installation (2.10.1 on Kubuntu Linux 910 64 >>> bit), >>> I keep getting the error: >>> >>> Error in nlsModel(formula, mf, start, wts, upper) : singular gradient >>> matrix at initial parameter estimates >>> >>> I have read all the previous postings and the documentation, but to no >>> avail: the error is there to stay. I am sure the problem is with nls, >>> because the external fitting algorithm perfectly fits it in less than a >>> second. Also, if my n is 4, then the nls works perfectly (but that >>> excludes >>> all the k5 .... kn). >>> >>> Can anyone help me with suggestions? Thanks in advance. >>> >>> Alternatively, what do you suggest I should do? Shall I abandon nls in >>> favour of optim? >>> >>> Regards >>> >>> -- >>> Corrado Topi >>> PhD Researcher >>> Global Climate Change and Biodiversity >>> Area 18,Department of Biology >>> University of York, York, YO10 5YW, UK >>> Phone: + 44 (0) 1904 328645, E-mail: ct...@york.ac.uk >>> >>> ______________________________________________ >>> 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. >>> >>> > > > -- > Corrado Topi > PhD Researcher > Global Climate Change and Biodiversity > Area 18,Department of Biology > University of York, York, YO10 5YW, UK > Phone: + 44 (0) 1904 328645, E-mail: ct...@york.ac.uk > >
______________________________________________ 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.