[Octave-bug-tracker] [bug #43551] Matlab incompatibility for gamma function for negative integer arguments

[Rik]

Follow-up Comment #3, bug #43551 (project octave):

That's kind of what I expected.  It does seem like it would be more useful to
return Inf and have terms go to zero.

I was just picking up the patch that someone had supplied so I don't know much
about the code.

The mod 2 thing seems to be trying to get the phase to be consistent for
negative integers.  The result of the gamma function is only infinite when x
is a negative integer (or when X itself is +Inf).  So the code, by checking
xisinf (result), is effectively deciding that x itself was a negative integer.
 The next test will determine whether x was an even or odd integer and will
flip the phase (+1,-1,+1,-1) to go with the absolute magnitude of infinity. 
This corresponds to consistently taking the limit from the right.

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