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From: "Alexander Babansky" <babansky@mail.ru>
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Subject: gsl-1.2
Date: Sun, 03 Nov 2002 07:17:00 -0000
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Hi,
I've found a small bug in Ei(x) function Reference manual(section
Exponential Integral)
In definition of Ei(x) it should be:
Ei(x) := - PV(\int_{-x}^\infty dt \exp(-t)/t)
(with "-" sign).

True mathematical definition of Ei(x) is:
Ei(x) :=  PV(\int_{-infinity}^x dt \exp(t)/t
When you change varibles, x-> -x you will get that "-" sign.
Bug is only in Reference manual not in Ei(x) itself.

Sincerely,
Alex