[R] Logistic regression

From: Guillaume Brutel <guillaume.brutel_at_yahoo.fr>
Date: Mon, 14 Apr 2008 17:51:42 +0200


Dear all,

I am trying to fit a non linear regression model to time series data.

If I do this:
reg.logis = nls(myVar~SSlogis(myTime,Asym,xmid,scal)) I get this error message (translated to English from French): Erreur in nls(y ~ 1/(1 + exp((xmid - x)/scal)), data = xy, start = list(xmid = aux[1], :

  le pas 0.000488281 became inferior to 'minFactor' of 0.000976562

I then tried to set the 'minFactor' value like this: reg.logis =
nls(myVar~SSlogis(myTime,Asym,xmid,scal),control=nls.control(minFactor=0.000488281)) But I have exactly the same error message, so it seems that the control was not changed

If I set some values for the SSlogis function like this: reg.logis=nls(myVar~SSlogis(myTime,Asym=25,xmid=600,scal=13)) or like this:
reg.logis=nls(myVar~SSlogis(myTime,Asym=25,xmid=600,scal=13),control=nls.control(minFactor=0.000488281)) I still have the same error message.

I have also tried with setting the starting value like this: reg.logis=nls(myVar~SSlogis(myTime,Asym=25,xmid=600,scal=13),control=nls.control(minFactor=0.000488281) + ,start=list(xmid=0,scal=13))
Bu then, I get this error message:
Error in nlsModel(formula, mf, start, wts) :   singular gradient matrix at initial parameter estimates

Could someone tell me what I am doing wrong? Many thanks
Guillaume.



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