[Octave-bug-tracker] [bug #47800] gammainc(x, a, "upper") rounds down to zero if output is below eps

[Marco Caliari]

Follow-up Comment #9, bug #47800 (project octave):

Thanks Nir,

but that code is quite inaccurate, try, for instance, gamain(2,3).
I started to implement, but how many corner cases! I used Numerical Recipes in
Fortran77 (chapter 6.2). It is possible to use either a series or a continued
fraction. I include my result, with some tests (the last still fails). Matlab
is generally better for large input values, unless completely wrong.
scaledupper and scaledlower options are not finished, yet. You can test it in
Matlab (no endif...). The reference values in the tests were taken by
wolframalpha. Don't know how to continue: modification of slatec functions
(reliable, but forget x<0) or fixing the m-file.

(file #37075)
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Additional Item Attachment:

File name: newgammainc.m                  Size:3 KB


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