# Definition:Graph of Mapping

## Definition

Let $S$ and $T$ be sets.

Let $f: S \to T$ be a mapping.

The graph of $f$ is the relation $\RR \subseteq S \times T$ defined as $\RR = \set {\tuple {x, \map f x}: x \in S}$

Alternatively, this can be expressed:

$G_f = \set {\tuple {s, t} \in S \times T: \map f s = t}$

where $G_f$ is the graph of $f$.

The word is usually used in the context of a diagram:

### Graph of Real Function

Let $U \subseteq \R^n$ be an open subset of $n$-dimensional Euclidean space.

Let $f : U \to \R^k$ be a real function.

The graph $\map \Gamma f$ of the function $f$ is the subset of $\R^n \times \R^k$ such that:

$\map \Gamma f = \set {\tuple {x, y} \in \R^n \times \R^k: x \in U \subseteq \R^n : \map f x = y}$

where $\times$ denotes the Cartesian product.

### Graph of Relation, also known as Truth Set

The concept can still be applied when $f$ is a relation, but in this case a vertical line through a point in the graph is not guaranteed to intersect the graph at one and only one point.

Let $\RR$ be a relation on $S \times T$.

The truth set of $\RR$ is the set of all ordered pairs $\tuple {s, t}$ of $S \times T$ such that $s \mathrel \RR t$:

$\map \TT \RR = \set {\tuple {s, t}: s \mathrel \RR t}$

## Also denoted as

The symbol $\Gamma_f$ is sometimes seen to denote the graph of $f$.

## Also see

• Results about Graphs of Mappings can be found here.