Apologize for not being clearer earlier. I would like to ask again. Thank
Joris and Markleeds for response.

Two examples:

1. Function 'var'. In R, it is the sum of square divided by (n-1) but not by
n. (I know this in R class)

2. Function 'lm'. In R, it is the residual sum of square divied by (n-2) not
by n, the same as in the least squares estimate. But the assumption
following that in the method of maximum likelihood.  (I know this by looking
up the book 'Introductory Statistics with R').

But not all functions are explained in the books.

I am thinking whether there is a general way to figure out how R function
works and what is the underlying theory besides looking at the codes
(type var or lm at the  Rprompt). Because R codes are too difficult to
understand.

Thanks

Yi

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