[Boost-bugs] [Boost C++ Libraries] #5433: beta function: when b<epsilon return tgamma(b)?

Subject: [Boost-bugs] [Boost C++ Libraries] #5433: beta function: when b<epsilon return tgamma(b)?
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2011-04-06 18:29:31

#5433: beta function: when b<epsilon return tgamma(b)?
----------------------------------------------+-----------------------------
 Reporter:  Eric Butter <egbutter@…>          |       Owner:  johnmaddock
     Type:  Bugs                              |      Status:  new        
Milestone:  To Be Determined                  |   Component:  math       
  Version:  Boost 1.47.0                      |    Severity:  Problem    
 Keywords:                                    |  
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 In the beta.hpp header for the beta function (i.e., *not* the beta
 distribution) around line 131, you have:

    if((c == a) && (b < tools::epsilon<T>()))
       return boost::math::tgamma(b, pol);
    else if((c == b) && (a < tools::epsilon<T>()))
       return boost::math::tgamma(a, pol);

 Don't you actually want if b<epsilon, tgamma(a)?  beta(a,b) reduces to
 (approximately) gamma(a)b^-a for a>>b, which seems like the case for which
 you are trying to account?

 Cheers,

 Eric

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/5433>
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