# Symbols:E/Expectation

## Expectation

$\expect X$

Let $X$ be a discrete random variable.

The expectation of $X$ is written $\expect X$, and is defined as:

$\expect X := \ds \sum_{x \mathop \in \image X} x \map \Pr {X = x}$

whenever the sum is absolutely convergent, that is, when:

$\ds \sum_{x \mathop \in \image X} \size {x \map \Pr {X = x} } < \infty$

The $\LaTeX$ code for $\expect X$ is \expect X .