[Octave-bug-tracker] [bug #39309] poisscdf fails for large arguments due to the algorithm in D9LGIT

[Thomas Weber]

URL:
  <http://savannah.gnu.org/bugs/?39309>

                 Summary: poisscdf fails for large arguments due to the
algorithm in D9LGIT
                 Project: GNU Octave
            Submitted by: tweber
            Submitted on: Fr 21 Jun 2013 11:28:33 GMT
                Category: Libraries
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Inaccurate Result
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 3.6.4
        Operating System: GNU/Linux

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Details:

Hi, 
this is an old bug report from Debian that I forward here in case someone
wants to spend some time on Fortran or GSL. Please note that John already
commented in the original bug report years ago.
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=418158

So, the issue is that 
poisscdf (604,604)
works, but
poisscdf (605,605)
fails with a Fortran error, as the algorithm did not converge. This is
ultimately due to the algorithm in libcruft/slatec-fn/d9lgit.f.

There was the suggestion to use the gamma_inc_P function from the gsl package,
but as far as I can see, this was never implemented.

Regards
Thomas





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