[R] Newbie Question: Shifted Power Fit?

[Douglas Bates]

Douglas Bates <bates at cs.wisc.edu> writes:

> Trying to evaluate the exponential of a negative number?  Think of how
> the expression (x-b)^c for non-integer c is evaluated when x = 3 and b
> = 3 - eps. 
    ^^^^^^^  Should be 3 + eps.  

The error occurs when using finite differences to evaluate the partial
derivative with respect to b.  If b = 3 + eps and x = 3 then (x-b)
is negative and (x-b)^pow returns NA.
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