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Interaction of Sum/Plus and KroneckerDelta

  • To: mathgroup at
  • Subject: [mg55178] Interaction of Sum/Plus and KroneckerDelta
  • From: "Ofek Shilon" <ofek at>
  • Date: Wed, 16 Mar 2005 05:35:53 -0500 (EST)
  • Sender: owner-wri-mathgroup at

I'm fighting Mathematica 5.1.0 to perform a (seemingly) elementary
simplification, and Mathematica - so far - wins, so i thought i'd
consult some veterans.
Here's a simplified example of the problem.

Sum[KroneckerDelta[i, j], {i, 1, 5}]

and you get:
KroneckerDelta[1, j] + KroneckerDelta[2, j] +
  KroneckerDelta[3, j] + KroneckerDelta[4, j] + KroneckerDelta[5, j]

which i want to simplify to 1.  The direct approach:
Simplify[%, Assumptions -> {j â?? Integers, 0 < j < 3}]

still gives:
KroneckerDelta[1, j] + KroneckerDelta[2, j]

Can Mathematica somehow automatically transform this to 1?
modification of the original sum are welcome too, of course.

  thanks for any ideas,

    Ofek Shilon

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