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Wrong result of Integrate with assumptions -- my fault?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg131395] Wrong result of Integrate with assumptions -- my fault?
  • From: Alain Cochard <Alain.Cochard at unistra.fr>
  • Date: Thu, 18 Jul 2013 03:01:07 -0400 (EDT)
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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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