This command generates the summation operator, $ \sum $. The difference between this and \Sigma, which generates the capital letter $ \Sigma $, is that \sum appears larger, and that it supports the limits to be displayed below and above the symbol.

The following example illustrates the difference between \sum and \Sigma. $ \sum_{n=1}^\infty\frac{1}{2^n}=1\qquad\Sigma_{n=1}^\infty\frac{1}{2^n}=1 $

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