| Author |
Comment/Response |
Andreas Veh
|
 09/10/00 12:38pm
Integrate[\[ExponentialE]^(-r/a), {r,0,\[Infinity]}]
yields an If[Re(a)>0, ...] . I know that I could use Abs[a] instead and would get the evaluated integral. But I have more problems of that sort where I need to tell it ''Let a>0, ...''. E.g.
Integrate[Exp[-r1]*r1^2*(Sqrt[(r1+r2)^2]-Sqrt[(r1-r2)^2])/r1/r2, {r1,0,Infinity}]
which is not evaluated.
The same integral can be rewritten: For r1<=r2, Integrate[Exp[-r1]*r1^2/r2, {r1,0,r2}] and for r1>=r2, Integrate[Exp[-r1], {r1,r2,Infinity}] which are evaluated. But how do I tell Mathematica ''For r1<=r2, Integrate[Exp[-r1]*r1^2*(Sqrt[(r1+r2)^2]-Sqrt[(r1-r2)^2])/r1/r2, {r1,0,r2}]'' etc.?
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