[R] nls segmented model with unknown joint points
andy
afinley at gis.umn.edu
Sun Apr 17 05:08:48 CEST 2005
Hello,
I am interested in fitting a segmented model with unknown joint points
in nls and perhaps eventually in nlme. I can fit this model in sas (see
below, joint points to be estimated are a41 and a41), but am unsure how
to specify this in the nlm function. I would really appreciate any
suggestions or example code. Thanks a lot. -andy
proc nlin data=Stems.Trees;
params b41=-3 b42=1.5 b43=-1.5 b44=50 a41=0.75 a42=0.1;
term1 = (b41*(x - 1) + b42*(x**2 -1));
if (a41 - x) >= 0 then
term2 = (b43*(a41 - x)**2);
else
term2 = 0;
if (a42 - x) >=0 then
term3 = (b44*(a42 - x)**2);
else
term3 = 0;
model y = term1+term2+term3;
run;
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