question on nls

["Tropmedres" <pan@tropmedres.ac>]

Hello

I am doing the curve fitting using the non-linear regression (nls). I am not
sure how to select the best model when I cannot get the AIC as in usual lm,
glm, gam model. I cannot use the stepAIC function from the MASS library
neither. For the nested models I have been using 'anova.nls with test=chisq'
but what about the non-nested models?

Thank you in advance

Wirichada