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case differentiation problem with "Assumptions"

  • To: mathgroup at smc.vnet.net
  • Subject: [mg83652] case differentiation problem with "Assumptions"
  • From: Paul.Wenk at googlemail.com
  • Date: Tue, 27 Nov 2007 06:14:39 -0500 (EST)

Hello,
I found the following problem using $Assumptions:
Let us calculate the integral: Integrate[Cos[(n \[Pi] (-W + y))/(2
W)]^2/W,{y,-W,W}]
for n \[Element] Integers and n>0 you receive 1, for n=0 you receive
2.
If you make the assumption
$Assumptions = n \[Element] Integers
then you get for the above integral the output 1, although for n=0
(also integer) it should be 2!
Why mathematica is not using a case differentiation in this case? How
is the information about the integer element inserted?

cheers,
Paul

p.s.
I'm using Mathematica 6.0.0 on Linux x86


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