Re: [Boost-bugs] [Boost C++ Libraries] #7290: complex acos is occasionally wrong

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #7290: complex acos is occasionally wrong
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2012-08-26 18:31:37

#7290: complex acos is occasionally wrong
--------------------------------------------------------------+-------------
  Reporter:  Stephen Montgomery-Smith <stephen@…>             |       Owner:  johnmaddock
      Type:  Bugs                                             |      Status:  new        
 Milestone:  To Be Determined                                 |   Component:  math       
   Version:  Boost 1.52.0                                     |    Severity:  Problem    
Resolution:                                                   |    Keywords:             
--------------------------------------------------------------+-------------

Comment (by Stephen Montgomery-Smith <stephen@…>):

 It looks like the mistake is in Figure 6 of the paper by Hull, Fairgrieve
 and Tang.  It looks like this patch fixes it.

 {{{
 diff -u boost-trunk/boost/math/complex/acos.hpp boost-trunk-
 new/boost/math/complex/acos.hpp
 --- boost-trunk/boost/math/complex/acos.hpp     2012-08-26
 18:24:02.000000000 +0000
 +++ boost-trunk-new/boost/math/complex/acos.hpp 2012-08-26
 18:25:48.000000000 +0000
 @@ -172,14 +172,15 @@
              }
              else
              {
 -               real = 0;
                 if(((std::numeric_limits<T>::max)() / xp1) > xm1)
                 {
                    // xp1 * xm1 won't overflow:
 +                  real = y / std::sqrt(xm1*xp1);
                    imag = boost::math::log1p(xm1 + std::sqrt(xp1*xm1));
                 }
                 else
                 {
 +                  real = y / x;
                    imag = log_two + std::log(x);
                 }
              }
 }}}

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/7290#comment:2>
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