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Math Help - Correct use of summation sign

  1. #1
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    Correct use of summation sign

    Hi!

    I just need to be sure I have used the summation sign correctly. That is:
    \sqrt{\sum_{i\not=j}^{n} A_{ij}^{2}}

    Correct me if I'm wrong, but this - when applied to a n x n matrix A - would be the square root of the sum of all individual elements squared, except the elements on the diagonal (where i = j); essentially the "length" of all elements (again without the diagonal).

    It's probably very easy, but I just want to make sure I'm not mistaken!

    Thank you in advance!
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  2. #2
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    Quote Originally Posted by Jodles View Post
    Hi!

    I just need to be sure I have used the summation sign correctly. That is:
    \sqrt{\sum_{i\not=j}^{n} A_{ij}^{2}}

    Correct me if I'm wrong, but this - when applied to a n x n matrix A - would be the square root of the sum of all individual elements squared, except the elements on the diagonal (where i = j); essentially the "length" of all elements (again without the diagonal).

    It's probably very easy, but I just want to make sure I'm not mistaken!

    Thank you in advance!

    It's fine but usually A_{ij} denotes the minors of the matrix A, so I'd rather write a non-capital a:

    \sqrt{\sum_{i\not=j}^{n} a_{ij}^{2}}

    Tonio
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  3. #3
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    Thank you, Tonio!
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