**Sum-class symbols**, or *accumulation symbols*, are symbols whose sub- and superscripts appear directly below and above the symbol rather than beside it. For example, the following example illustrates that `\sum`

is one of these elite symbols whereas `\Sigma`

is not. The terminology from AMS-LaTeX documentation.

### Table of sum-class symbolsEdit

### Using sumEdit

LaTeX markup... | ...results in: | ...is used for: |
---|---|---|

`\sum\limits_{i=1}^n i^2 = \frac{n(n+1)(2n+1)}{6}`
| the \limits tag puts the limits below and above the sigma symbol. It is typically used in equations | |

`\sum\nolimits_{P_i \in Paths(I)} Probes(P_{i})`
| the \nolimits tag puts the limits on the right of the sigma symbol. It is typically used in the math wired in the text |

TeX is smart enough to only show `\sum`

in its expanded form in the displaymath environment. In the regular math environment, `\sum`

does the right thing and revert to non-sum-class behavior, thus conserving vertical space.

### Using prodEdit

Another common sum-class symbol is `\prod`

. As in `\sum`

we can use the directive `\limits`

or `\nolimits`

in order to show the limits on top-down or on the right.

LaTeX markup... | ...results in: | ...is used for: |
---|---|---|

`\prod\limits_{i=1}^n x = x^n`
| the product of a sequence of factors |