R help - Jul 2009 - Non-Linear Regression with two Predictors

Hello there,

I am using nls the first time for a non-linear regression with a 
logistic growth function:
startparam <- c(alpha=3e+07,beta=4000,gamma=2)
fit <- nls(dataset$V2~(( alpha / ( 1 + exp( beta - gamma * dataset$V1 ) 
) ) ),data=dataset,start=startparam)

Everything works fine and i get good results. Now I would like to 
improve the results using my DUMMY Variable (dataset$V6) the runs half 
of the time 0 and then 1. This is my new nls:
startparam <- c(alpha=3e+07,beta=4000,gamma=2,delta=1000000)
fit <- nls(dataset$V2~(( alpha / ( 1 + exp( beta - gamma * dataset$V1 ) 
) ) + (dataset$V6*dataset$V1*delta) ),data=dataset,start=startparam)

I get "Singular Gradient Matrice". May anyone give me the right nls 
function for this problem??

Regards

Hi and thank you for your reply,

in my new regression formular the parameter delta is inserted:
fit <- nls(dataset$V2~(( alpha / ( 1 + exp( beta - gamma* dataset$V1 ) ) 
) + (dataset$V6*delta)),data=dataset,start=startparam)

The sense is, that dataset$V6 is a dummy variable that represents the 
german reunion. I expect, that the delta in the regression is about 
1.000.000 because of the reunion. The logistic function thus has a jump 
at this point. But I would like to get the exact paramter value for 
delta (the jump) as the parameters for the logistic function of growth 
(alpha to gamma). The partial derivative to delta would be like a 
stair-function. It is 0 until 1990 and 1 there after.

Any idea? Thank you!

Regards

Moshe Olshansky schrieb:
> Hi,
>
> I believe that since delta does not appear in the function you are
optimizing, it's partial derivative with respect to delta is always 0 and so
the gradient is singular.
> Why do you need delta at all?
>
> --- On Mon, 27/7/09, Berlinerfee <berlinerfee@yahoo.de> wrote:
>
>   
>> From: Berlinerfee <berlinerfee@yahoo.de>
>> Subject: [R] Non-Linear Regression with two Predictors
>> To: R-help@stat.math.ethz.ch
>> Received: Monday, 27 July, 2009, 2:52 AM
>> Hello there,
>>
>> I am using nls the first time for a non-linear regression
>> with a logistic growth function:
>> startparam <- c(alpha=3e+07,beta=4000,gamma=2)
>> fit <- nls(dataset$V2~(( alpha / ( 1 + exp( beta - gamma
>> * dataset$V1 ) ) ) ),data=dataset,start=startparam)
>>
>> Everything works fine and i get good results. Now I would
>> like to improve the results using my DUMMY Variable
>> (dataset$V6) the runs half of the time 0 and then 1. This is
>> my new nls:
>> startparam <-
>> c(alpha=3e+07,beta=4000,gamma=2,delta=1000000)
>> fit <- nls(dataset$V2~(( alpha / ( 1 + exp( beta - gamma
>> * dataset$V1 ) ) ) + (dataset$V6*dataset$V1*delta)
>> ),data=dataset,start=startparam)
>>
>> I get "Singular Gradient Matrice". May anyone give me the
>> right nls function for this problem??
>>
>> Regards
>>
>> ______________________________________________
>> R-help@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.
>>
>>     
>
>   

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