# Definition:Supremum Norm

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## Definition

Let $S$ be a set.

Let $\struct {X, \norm {\,\cdot\,} }$ be a normed vector space.

Let $\BB$ be the set of bounded mappings $S \to X$.

For $f \in \BB$ the **supremum norm** of $f$ on $S$ is defined as:

- $\norm f_\infty = \sup \set {\norm {\map f x}: x \in S}$

### Supremum Norm on Continuous on Closed Interval Real-Valued Functions

Let $I = \closedint a b$ be a closed real interval.

Let $\map C I$ be the space of real-valued functions continuous on $I$.

Let $f \in \map C I$.

Let $\size {\, \cdot \,}$ denote the absolute value.

Suppose $\sup$ denotes the supremum of real-valued functions.

Then the **supremum norm** over $\map C I$ is defined as

- $\ds \norm {f}_\infty := \sup_{x \mathop \in I} \size {\map f x}$

## Also known as

Other names include the **sup norm**, **uniform norm** or **infinity norm**.