Are there any functions to do error propagation in R?

I have done a search with little success. Any

pointers to read about this topic are greatly

welcomed.

My specific problem is: I use a linear model (lm) to

predict the biomass of an individual in a population,

then I add up the biomass of all individuals to

calculate the total mass of the population. I want to

calculate the error in the final estimate of the total

biomass.

Also, I have another case where I use a nls model

instead of the lm, but in nls se.fit is currently

ignored as stated in the help page. Is there an

alternative way to calculate the errors in the

predictions from nls?

Thanks,

Manuel

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