# Definition:Pointwise Scalar Multiplication of Rational-Valued Function

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## Definition

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:

- $\lambda \times f: S \to \Q:$
- $\forall s \in S: \map {\paren {\lambda \times f} } s := \lambda \times \map f s$

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:

- $f_\lambda: S \to \Q: \map {f_\lambda} s = \lambda$

## Also denoted as

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

- $\forall s \in S: \map {\paren {\lambda \cdot f} } s := \lambda \cdot \map f s$

or:

- $\forall s \in S: \map {\paren {\lambda f} } s := \lambda \map f s$

## Also see

- Definition:Pointwise Addition of Rational-Valued Functions
- Definition:Pointwise Multiplication of Rational-Valued Functions

- Definition:Pointwise Scalar Multiplication of Number-Valued Function: a more general concept of which this is a specific instance