[R] nls power law help

[Prof J C Nash (U30A)]

With minor corrections, the original problem can be "solved" with nlxb 
from nlmrt package.

 > coef(modeln)
           a           b
  -0.8470857 409.5190808

ssquares =  145585533

but since

 > svd(modeln$jacobian)$d
[1] 5.128345e+04 6.049076e-14
 >

I may have made nlmrt too robust.

JN



On 13-07-15 06:00 AM, r-help-request at r-project.org wrote:
> Message: 9
> Date: Sun, 14 Jul 2013 16:11:40 +0100
> From: Prof Brian Ripley<ripley at stats.ox.ac.uk>
> To:r-help at r-project.org
> Subject: Re: [R] nls power law help
> Message-ID:<51E2BFAC.1010008 at stats.ox.ac.uk>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> On 14/07/2013 14:30, JenPool wrote:
>> >Hi,
>> >
>> >I am trying to use a power law y=bx^a as a nls model as below, however I
>> >keep getting 'singular gradient' error. I have tried multiple different
>> >starting values but always get an error.
> That is not the model you tried to fit. b*x*exp(a) is always
> over-parametrized.