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authorvlefevre <vlefevre@280ebfd0-de03-0410-8827-d642c229c3f4>2017-04-03 09:16:27 +0000
committervlefevre <vlefevre@280ebfd0-de03-0410-8827-d642c229c3f4>2017-04-03 09:16:27 +0000
commit1543c40a4bf927230a0f93236f71688647a2ff32 (patch)
treeb87a4d59ec2a8ad4b053aeee9da6b4b319c36f2d /TODO
parent5e952138d666c5f9ecef9d29ebd081bb6448204d (diff)
downloadmpfr-1543c40a4bf927230a0f93236f71688647a2ff32.tar.gz
[TODO,src/atanh.c] Suggest a faster formula for atanh(x) on small x.
git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@11398 280ebfd0-de03-0410-8827-d642c229c3f4
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Also mpfr_div uses the remainder computed by mpn_divrem. A workaround would
be to first try with mpn_div_q, and if we cannot (easily) compute the
rounding, then use the current code with mpn_divrem.
+- improve atanh(x) for small x by using atanh(x) = log1p(2x/(1-x)).
- compute exp by using the series for cosh or sinh, which has half the terms
(see Exercise 4.11 from Modern Computer Arithmetic, version 0.3)
The same method can be used for log, using the series for atanh, i.e.,