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