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Integration of Ei function

GROUPS:
Hi,
I want to integrate the function Exp/(B-x) for x, within the limits 0 to N. What I could figure out by now is that I have to use ExpIntegralEi function for such kind of integrations in mathematica, but not able to get the complete solution. Please let me know how could I get my integration done.

thanks
SHG
POSTED BY: S G
Answer
6 months ago
It works for me on version 9.0.1
Integrate[Exp[a*x]/(b - x), {x, 0, n}]

ConditionalExpression[
E^(a b) (-Gamma[0, a b] + Gamma[0, a (b - n)] + Log[b] - Log[a b] -
    Log[b - n] + Log[a (b - n)]),  Im[b/n] != 0 || Re[b/n] > 1 || Re[b/n] < 0]
Could you show what you actually typed? It is better to use lower case letters. Also "N" is reserved symbol in Mathematica.
POSTED BY: Nasser
Answer
6 months ago
The standered form of Ei function is, Ei(z) = -Integrate[Exp[-t]/t, {t, -z,  infinite].  But for the function I am trying to integrate, this needs to be modified..
POSTED BY: S G
Answer
6 months ago