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[Octave-patch-tracker] [patch #9549] Improve expint handled of signed ze

From: Rik
Subject: [Octave-patch-tracker] [patch #9549] Improve expint handled of signed zero
Date: Tue, 11 Dec 2018 11:47:13 -0500 (EST)
User-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.116 Safari/537.36 Edge/15.15063

Follow-up Comment #4, patch #9549 (project octave):

So currently Matlab and Octave are compatible.  Is it more useful to be
mathematically correct, or compatible?  Here is a bit of testing I did in

octave:1> expint (-0)
ans =  Inf
octave:2> expint (-1e-6)
ans =  13.2383 -  3.1416i
octave:3> expint (-1e-8)
ans =  17.8435 -  3.1416i
octave:4> expint (-1e-9)
ans =  20.1461 -  3.1416i
octave:5> expint (-1e-10)
ans =  22.4486 -  3.1416i
octave:6> expint (1e-10)
ans =  22.449
octave:7> expint (1e-11)
ans =  24.751
octave:8> expint (-1e-11)
ans =  24.7512 -  3.1416i

If the expint function is continuous then as you approach 0 from the negative
direction it does seem like the value should converge to complex (Inf, -pi) as
the first changeset does.  But, you know there are a bunch of Matlab folks who
will whine if the result is not exactly the same.


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