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Topic: Wrong result of Integrate with assumptions -- my fault?
Replies: 3   Last Post: Sep 11, 2013 3:44 AM

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Alain Cochard

Posts: 7
Registered: 5/6/13
Wrong result of Integrate with assumptions -- my fault?
Posted: Jul 18, 2013 2:44 AM
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Dear group --

In the following, it seems adding the assumption that w is real spoils
the result:

res1=Integrate[t*Exp[I w t],{t,a,b}, Assumptions-> a<b] ;
res2=Integrate[t*Exp[I w t],{t,a,b}, Assumptions-> a<b && Element[w,Reals]];
Chop[N[res1-res2/.{a->-1, b->2, w->3}]]

gives 0. + 0.691355 I (I tried Mathematica 7, 8, 9 installed on 3 different
GNU/Linux machines).

>From the various tests I did, it seems that the real parts are always
identical while the imaginary parts differ in the case a < 0.

Was this to be expected? Am I not allowed to make this assumption?

Thank you.

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