the meaning of a mathematical symbol

Could someone please tell me what the symbol which looks like E (for example in http://en.wikipedia.org/math/1362f6b...1017183c17.png) means? I keep seeing this symbol, and I am very curious.

Thanks!

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.

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
http://www.andrews.edu/~calkins/ mat...xts/factor.gif

Thanks! You guys are such awsome geeks!

Quote:

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Originally posted by Evil_Cowgod
Thanks! You guys are such awsome geeks!

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Thanks for the compliment, Evil Cowgod! I've always felt geeky, but no one's confirmed it until now! ;)

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?