This command generates the summation operator,

. The difference between this and \Sigma, which generates the capital letter

, 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.

This examples are written as:

1 \sum_{n=1}^\infty\frac{1}{2^n}=1
2 \qquad
3 \Sigma_{n=1}^\infty\frac{1}{2^n}=1
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