[Octave-bug-tracker] [bug #60528] special function: betaincinv

[Rik]

Update of bug #60528 (project octave):

                  Status:                    None => Ready For Test         
        Operating System:       Microsoft Windows => Any                    

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Follow-up Comment #1:

Confirmed.  The code in betaincinv uses a Newton's Method search.  As part of
that process intermediate guesses can fall below zero.  I fixed that in this
changeset http://hg.savannah.gnu.org/hgweb/octave/rev/26ba91f0eea7.

The code I used was


  x(x(todo) < 0) = eps;  # Avoid negative x in betainc() call, bug #60528


where I moved any intermediate guess that was negative to be just greater than
0.

Of course, that made me wonder if it was possible for intermediate values to
exceed 1.0 and that was also true.  So I had to add another line


  x(x(todo) > 1) = 1-eps;


See additional changeset
http://hg.savannah.gnu.org/hgweb/octave/rev/69b6b783a8ab.

Marking as Ready for Test.  You can download the m-file from the Mercurial
repository and copy it over your existing betaincinv.m to see the changes.

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