# Definition:Pointwise Scalar Multiplication of Rational-Valued Function

## Definition

Let $S$ be a non-empty set.

Let $f: S \to \Q$ be an rational-valued function.

Let $\lambda \in \Q$ be an rational number.

Then the pointwise scalar product of $f$ by $\lambda$ is defined as:

$\lambda \times f: S \to \Q:$
$\forall s \in S: \left({\lambda \times f}\right) \left({s}\right) := \lambda \times f \left({s}\right)$

where the $\times$ on the right hand side is rational multiplication.

This can be seen to be an instance of pointwise multiplication where one of the functions is the constant mapping:

$f_\lambda: S \to \Q: f_\lambda \left({s}\right) = \lambda$

## Also denoted as

Using the other common notational forms for multiplication, this definition can also be written:

$\forall s \in S: \left({\lambda \cdot f}\right) \left({s}\right) := \lambda \cdot f \left({s}\right)$

or:

$\forall s \in S: \left({\lambda f}\right) \left({s}\right) := \lambda f \left({s}\right)$