[R] Non-linear regression analysis in R

[Jeremy Miles]

Could you provide the code that you're running, so we can see what
you're trying to do?  Even better would be a repeatable example.

Jeremy

On 19 December 2012 09:42, Yann Labou <yann.labou at outlook.com> wrote:
> 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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