Indicator Function - Definition

Definition

The indicator function of a subset of a set is a function

defined as

\mathbf{1}_A(x) =
\begin{cases}
1 &\text{if } x \in A, \\
0 &\text{if } x \notin A.
\end{cases}

The Iverson bracket allows the equivalent notation, to be used instead of

The function is sometimes denoted or or even just . (The Greek letter χ appears because it is the initial letter of the Greek word characteristic.)

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