>>>>> "Robert" == Robert Dodier <robert.dodier at gmail.com> writes:
Robert> Barton,
>> (4) sbcl, clispm and cmucl users are going to be
>> disappointed when they discover that atanh evaluates
>> using (log(1 + x) - log(1 - x)) / 2;
Robert> We can easily fix this by punting to cl:atanh for any input
Robert> not on a branch cut.
f(x) := (log(1+x)-log(1-x))/2$
realpart(f(1d5));
1.0000000000509601e-5
:lisp (realpart (cl:atanh 1d5))
1.0000000000333332e-5
Assuming I did this right f(x) should be about log(1+2/(x-1))/2 for
large x. This produces an answer similar to Lisp's answer.
Close, but we should do better than this.
Ray