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Regarding Einstein Summation Convention

  1. Sep 30, 2012 #1
    So, I realize the basic theory behind Einstein Summation Convention is that any repeated set of indices implicitly indicates a sum over those indices. However, what if an index is repeated three times?

    For example, my mathematics professor posted this problem:

    εijkajaj = ?

    As you can see, j is repeated thrice. So how do I approach this?
  2. jcsd
  3. Oct 1, 2012 #2


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    It's nothing to approach, it's incorrect. In a monomial (product of indexed objects) an index can appear no more than 2 times.
  4. Oct 1, 2012 #3


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    It looks like a simple error. ajaj should be aiaj
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