[R] Error "singular gradient matrix at initial parameter

[Corrado]

Yes, of course. The problem still stays.

Gabor Grothendieck wrote:
> 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
>>
>>
>>     


-- 
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