[R] Error "singular gradient matrix at initial parameter

[Corrado]

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
>>
>> ______________________________________________
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>> 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