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st: nl-function log4-formula


From   Jennyfer Wolf <[email protected]>
To   [email protected]
Subject   st: nl-function log4-formula
Date   Wed, 16 Nov 2011 11:28:50 +0100

Dear all,
I am working with the nl-function and with the logistic function model log 4.
Could somebody please explain me why I do not get the same outout if I type:

1. nl log4: VAR1 VAR2 if VAR3=="xxx"

and

2. nl(VAR1={b0}+{b1}/(1+exp(-{b2}*(VAR2-{b3}))) if VAR3=="xxx")

Actually 1. should just be an abbreviation of 2.?
If I run command 1, I get estimates for b0, b1, b2, b3, if I run
command 2 I only get an estimate for b0 and b1-b3 are 0.

Could somebody explain how to write the formula "in full" (like in
2.), to get the same results as in the first formula.

Thank you very much!
Jennyfer
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