[Developers] incomplete beta function is broken

[John Sibert]

I share Dave's concern about simply changing functions. Using capitals 
to distinguish versions is one solution. Using a namespace is an 
alternative, if vaguely annoying, solution. (I'm annoyed every time in 
need to specify a namespace to use cout,) The namepasce Cephes is 
already in use. It would make it easy to compare results with the 
appropriate using namespace declaration.

More generally, the lack of smoothness is probably a result of the 
polynomial approximation. May functions use such approximations. Is this 
a commonly encountered problem? Or does it mainly occur at the extremes 
of the function's domain?

John

John Sibert
Emeritus Researcher, SOEST
University of Hawaii at Manoa

Visit the ADMB project http://admb-project.org/


On 06/27/2012 05:03 AM, dave fournier wrote:
> As I noted earlier the cephes version of the beta (and probably  log 
> gamma) functions
> appear to lack sufficient smoothess for the random effects stuff.    
> The solution is to go
> back to the versions based on NR.  However rather than replacing them 
> I think it would be
> easier to simply add the old functions to the package with a slight 
> name change.
> Could use capitals as Betai, Gammln. Then both versions would be 
> available and
> experience would show which are best for various applications.  Any 
> thoughts?
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