R help - Mar 2013 - Constrain slope in segmented package

Hello,

I'm currently using the segmented package of M.R. Muggeo to fit a 
two-slope segmented regression. I would like to constrain a 
null-left-slope, but I cannot make it. I followed the explanations of 
the package (http://dssm.unipa.it/vmuggeo/segmentedRnews.pdf) to write 
the following code :

   fit.glm <- glm(y~x)
   fit.seg <- segmented(fit.glm, seg.Z=~x,psi=0.3)
   fit.glm <-update(fit.glm,.~.-x)
   fit.seg1 <-update(fit.seg)

If I got well, the two last lines are supposed to constrain the slope, 
but it did not change anything. Could you help me with this ?
By the way, I don't understand the ".-.-x" code in the update
function.

Thanks a lot by anticipation !

Pierre

-- 
Pierre Hainaut
Université Catholique de Louvain
Earth and Life Institute
Croix du Sud, 2 - bât. De Serres, B337 - bte L7.05.14
1348 Louvain-la-Neuve - Belgique
+3210479326


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On 2013-03-12 03:55, Pierre Hainaut wrote:
> Hello,
>
> I'm currently using the segmented package of M.R. Muggeo to fit a
> two-slope segmented regression. I would like to constrain a
> null-left-slope, but I cannot make it. I followed the explanations of
> the package (http://dssm.unipa.it/vmuggeo/segmentedRnews.pdf) to write
> the following code :
>
>     fit.glm <- glm(y~x)
>     fit.seg <- segmented(fit.glm, seg.Z=~x,psi=0.3)
>     fit.glm <-update(fit.glm,.~.-x)
>     fit.seg1 <-update(fit.seg)
>
> If I got well, the two last lines are supposed to constrain the slope,
> but it did not change anything. Could you help me with this ?
> By the way, I don't understand the ".-.-x" code in the update
function.
>
> Thanks a lot by anticipation !
>
> Pierre
>
I can't help you with the segmented constraints, but the
'dot'-notation
is very well and concisely documented: use ?update which will take you
to a link for ?update.formula where you can read all about it.

Peter Ehlers