Definition:Step Function

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Definition

A real function $f: \R \to \R$ is a step function if and only if it can be expressed as a finite linear combination of the form:

$\map f x = \lambda_1 \chi_{\mathbb I_1} + \lambda_2 \chi_{\mathbb I_2} + \cdots + \lambda_n \chi_{\mathbb I_n}$

where:

$\lambda_1, \lambda_2, \ldots, \lambda_n$ are real constants

$\mathbb I_1, \mathbb I_2, \ldots, \mathbb I_n$ are open intervals, where these intervals partition $\R$ (except for the endpoints)

$\chi_{\mathbb I_1}, \chi_{\mathbb I_2}, \ldots, \chi_{\mathbb I_n}$ are characteristic functions of $\mathbb I_1, \mathbb I_2, \ldots, \mathbb I_n$.

Also see

• Definition:Heaviside Step Function

Sources

• 1961: I.N. Sneddon: Fourier Series ... (previous) ... (next): Chapter One: $\S 2$. Fourier Series

• Weisstein, Eric W. "Step Function." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/StepFunction.html
• This article incorporates material from simple functions on PlanetMath, which is licensed under the Creative Commons Attribution/Share-Alike License.