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Homework Help: Qm notation

  1. Aug 31, 2012 #1
  2. jcsd
  3. Aug 31, 2012 #2
    Do you know what the brackets mean in general?

    Edit: pay attention to this line in particular.

    This tells you very explicitly what the interpretation of both quantities should be.
  4. Aug 31, 2012 #3
    I didn't see that sentence the square of the average is not the same as the average of squares. But now i do.
  5. Aug 31, 2012 #4
    Nevertheless I'm truly amazed that you saw the question almost the moment I posted it and answered it in about 5 seconds. Wow!
  6. Aug 31, 2012 #5


    Staff: Mentor

    I think the <> notation just means average.

    so the <j^2> means the average of the squares of j values

    and <j>^2 is the square of the average of j values
  7. Aug 31, 2012 #6
    But I guess what the brackets mean is that you have the take the average of what is between them, so pretend { is a bracket. If you know the latex for brackets please let me know.

    {j^2} where j is 2,3,4 would be the average of 4 9 16 hence a little above 9 whereas {j}^2 would be 9 exactly, right?
  8. Aug 31, 2012 #7
    Use \langle and \rangle for pretty brackets (not horrendously bad ones, which are what <> give you).

    Otherwise, yes, you have the basic idea now. You should be accustomed to seeing [itex]\langle j^2 \rangle - \langle j \rangle^2 = \sigma_j^2[/itex] as well. This is one formula for the variance.
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