[R] nls: singular convergeance

[Redding, Matthew]

Hi Rolf and others, 

Once again, I think a misunderstanding. My inexperience has led me to
use the 
term "broken stick" where "non-linear segments" might be more
appropriate.

This is all experimental data (t and seg_an), and yes I am fitting a
model to this data (see the "crv" function in
my example).

Fitting three linear segments to the data won't provide the parameter
estimates required.
The functions suiting this data are theoretically non-linear.  However,
I guess I have learned 
that ultimately I needed 
to collect measurements for longer until the non-linearity of 
each segment becomes more obvious. 

So I guess no amount of tweaking nls will help!

Thanks for your time.

Kind regards, 

Matt Redding







>-----Original Message-----
>From: Rolf Turner [mailto:rolf.turner at xtra.co.nz] 
>Sent: Friday, 14 October 2011 9:10 AM
>To: Redding, Matthew
>Cc: r-help at r-project.org
>Subject: Re: [R] nls: singular convergeance
>
>On 14/10/11 11:39, Redding, Matthew wrote:
>> Hi Rolf and Others,
>>
>> Thanks Rolf for your suggestion.
>> I've had a look at segmented, but can't see how it can help.
>>
>> My model is the solution to an ODE of a physical system. The fitted 
>> parameters from this model are the answers I require.
>>
>> I'm not sure how segmented can help -- it is a linear 
>regression tool. 
>> Can you let me know how it could be used?
>
>No I can't. You said you were trying to fit a "broken stick" 
>model, which is what the "segmented" package does.  If you are 
>not fitting a model to data, then I have no idea as to how you 
>might proceed.
>
>You have to make it much more clear what you are trying to do 
>before I (or anyone) can make constructive suggestions.
>
>     cheers,
>
>         Rolf Turner
>
>
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