[R] Non-linear regression analysis in R
Yann Labou
yann.labou at outlook.com
Wed Dec 19 18:42:16 CET 2012
Hey all,
I'm trying to fit a non-linear model y ~ a * constant ^ b * x ^ c and
estimates the paramaters a, b and c.
Using the nls function, I'm getting following error message:
Error in nlsModel(formula, mf, start, wts) :
singular gradient matrix at initial parameter estimates
If I logarithmize the whole equation log(y) ~ log (a) + b *
log(constant) + c * log(x) and fit the equation with lm, I get only NAs
estimates for the second term on the right side:
Coefficients: (1 not defined because of singularities)
Do you have any hints on how to fit this equation or any alternatives to
nls?
Thanks,
Yann
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