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Thread: the meaning of a mathematical symbol

  1. Apr 7th, 2004, 01:13 AM #1
    Evil_Cowgod
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    the meaning of a mathematical symbol

    Could someone please tell me what the symbol which looks like E (for example in ) means? I keep seeing this symbol, and I am very curious.

    Thanks!
    Last edited by Evil_Cowgod; Apr 7th, 2004 at 01:17 AM.
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  2. Apr 7th, 2004, 05:10 AM #2
    azteched
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    it means "sum"

    so in that picture, H is the sum of all the values of (p*log(p)) for however many p-values you have.
    an ending
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  3. Apr 7th, 2004, 06:21 AM #3
    jskog
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    more math

    Azteched is right, it means sum, and the greek letter is called capital sigma.
    The index i below the sigma means you are supposed to sum for all indeces i in your set. In case you'd have for instance i=0 below the sigma and a 5 above, it means "sum for all indeces i=0 to 5".

    BTW, there is also another similar symbol meaning "product". That letter is the capital pi, and it looks like
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  4. Apr 7th, 2004, 09:39 PM #4
    Evil_Cowgod
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    Thanks! You guys are such awsome geeks!
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  6. Apr 8th, 2004, 03:26 AM #5
    jskog
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    Originally posted by Evil_Cowgod
    Thanks! You guys are such awsome geeks!
    Thanks for the compliment, Evil Cowgod! I've always felt geeky, but no one's confirmed it until now!
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  7. Apr 9th, 2004, 02:36 PM #6
    kedaman
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    and that formula is the definition of entropy btw, defined in information theory, which is a field of interest for me, so out of interest what are you up to?
    Use
    writing software in C++ is like driving rivets into steel beam with a toothpick.
    writing haskell makes your life easier:
    reverse (p (6*9)) where p x|x==0=""|True=chr (48+z): p y where (y,z)=divMod x 13
    To throw away OOP for low level languages is myopia, to keep OOP is hyperopia. To throw away OOP for a high level language is insight.
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