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Notation question - what does ! mean?

  1. Oct 8, 2009 #1
    Notation question - what does "!" mean?

    1. The problem statement, all variables and given/known data
    Hi, this is part of a question, in the context of rotation of the Lagrangian:

    x_i -> [tex]O[/tex]_ij.x_j, summation over j !

    My question is: what does the " !" after the j mean?

    Thanks

    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Oct 8, 2009 #2

    tiny-tim

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    Hi Pyroadept! :smile:

    (try using the X2 tag just above the Reply box :wink:)

    xi -> Oijxj is written in the "Einstein summation convention", where any repeated index is summed over.

    I don't think the ! means anything, except happiness ! :smile:
     
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