Symbols:Greek/Sigma

Event Space

 * $\Sigma$

Summation
Let $\left({S, +}\right)$ be an algebraic structure where the operation $+$ is an operation derived from, or arising from, the addition operation on the natural numbers.

Let $\left({a_1, a_2, \ldots, a_n}\right) \in S^n$ be an ordered $n$-tuple in $S$.

The composite is called the summation of $\left({a_1, a_2, \ldots, a_n}\right)$, and is written:


 * $\displaystyle \sum_{j \mathop = 1}^n a_j = \left({a_1 + a_2 + \cdots + a_n}\right)$

Sigma Function

 * $\sigma \left({n}\right)$

Surface Charge Density

 * $\sigma$

Used to denote the surface charge density of a given body:
 * $\displaystyle \sigma = \frac q A$

where:
 * $q$ is the body's electric charge;
 * $A$ is the body's area.

Area Density

 * $\sigma$

Used sometimes, although $\rho_A$ (Greek letter rho) is more common, to denote the area density of a given two-dimensional body:
 * $\sigma = \dfrac m A$

where:
 * $m$ is the body's mass;
 * $A$ is the body's area.