
Dear
I have a data.frame, and want to fit a constrained non-linear model:
data:






x
y

-0.08
20.815

-0.065
19.8128

-0.05
19.1824

-0.03
18.7346

-0.015
18.3129

0.015
18.0269

0.03
18.4715

0.05
18.9517

0.065
19.4184

0.08
20.146

0
18.2947
model:
y~exp(a)*(x-m)^4+exp(b)*(x-m)^2+const
 
I try to use nls() and set start=list(a=1,b=1,c=1,m=1), but which always give me a error message that " Error in qr.solv(QR.B,cc): singular matrix 'a' in solve". How can i build a selfStart? or any suggestion!
 
Thanks&Regards,
Vina
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