[R] Error "singular gradient matrix at initial parameter

[Gabor Grothendieck]

Sorry, its algorithm="brute-force"

On Tue, Mar 30, 2010 at 10:29 AM, Corrado <ct529 at 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 <ct529 at 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: ct529 at york.ac.uk
>>>
>>> ______________________________________________
>>> R-help at 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: ct529 at york.ac.uk
>
>