Definition:Pointwise Addition of Mappings

Definition

Let $X$ be a nonempty set, and let $\left({G, \circ}\right)$ be a magma.

Let $G^X$ be the set of all mappings from $X$ to $G$.

Then pointwise addition on $G^X$ is the binary map $\circ: G^X \times G^X \to G^X$ (the $\circ$ is the same as for $G$) defined by:

$\forall f,g \in G^X, x \in X: \left({f \circ g}\right) \left({x}\right) := f \left({x}\right) \circ g \left({x}\right)$

It is clear that $f \circ g \in G^X$, hence $\left({G^X, \circ}\right)$ is a magma.

The double use of $\circ$ is justified as $\left({G^X, \circ}\right)$ inherits all abstract-algebraic properties $\left({G, \circ}\right)$ might have.

For example, $G^X$ is a group precisely when $G$ is.

Pointwise Multiplication

Let $\circ$ be used with multiplicative notation.

Then the operation defined above is called pointwise multiplication instead.

See also

• Pointwise Scalar Multiplication of Mappings, a similar concept commonly used with maps on vector spaces.