# Revision history [back]

Incomplete Gamma function and the Ei function are indeed related. See the following pages for example.

http://en.wikipedia.org/wiki/Exponential_integral http://en.wikipedia.org/wiki/Incomplete_gamma_function

In this sense, the result of the integration is correct.

There is indeed a subtly of brunch cut. Maxima / Sage defines the brunch cut of the function differently from Mathematica. I tested the Maxima result "-1/x + Ei(x) - gamma(-1, -x)" is indeed continuous on the complex plane. But the same function in Mathematica is not continuous.

Incomplete Gamma function and the Ei function are indeed related. See the following pages for example.

http://en.wikipedia.org/wiki/Exponential_integral http://en.wikipedia.org/wiki/Incomplete_gamma_function

In this sense, the result of the integration is correct.

There is indeed a subtly of brunch cut. Maxima / Sage defines the brunch cut of the function differently from Mathematica. I tested the Maxima result "-1/x + Ei(x) - gamma(-1, -x)" is indeed continuous on the complex plane. plane (i.e. the result has no problem). But the same function in Mathematica is not continuous.