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

[Colin Macdonald]

Follow-up Comment #11, bug #47800 (project octave):

In case it helps with development, I've just added gammainc to Symbolic. 
Here's a useful recipe for experimenting:


>> xs = sym (20); x = double (xs); a = 1;
>> A = gammainc (x, a, 'upper')
A =    2.0612e-09
>> B = double (gammainc (xs, a, 'upper'))
B =    2.0612e-09
>> relerr = (A-B)/abs(B)
relerr =   -2.0034e-08


I also put some 'xtest' BIST into '@sym/gammainc' that should pass once this
bug is fixed.

I'm worried about the state of special functions in Octave :(


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