What is Step Function?

Dhristi JEE 2022-24

Step Function

A step function is explained as a finite linear combination of indicator functions for given intervals. A step function is also known as the Greatest Integer Function or Floor Function. However, it is a discontinuous function. Students may come across the step functions while learning other types of functions, for example, sign function “sgn(x)”, Heaviside Function, and Rectangular function, etc. The step function is used to coordinate session-based applications. For example, it can be used to coordinate all the steps of a checkout process on an e-commerce site. A step function f: R → R can be written in the form:


\[ f(x) = \sum _{ i = 0}^{n} \alpha _{i} X_{Ai}(x)\]


for all real numbers x. 


If n ≥ 0, αi are real numbers and Ai are intervals, then the indicator function of A is χA, and it can be written as below:


\[X_{A}(x) = \left\{\begin{matrix} 1; if x \in A, &  & \\ 0; if x \notin A, &  & \end{matrix}\right.\]


Unit Step Function Definition

Unit Step Function is also known as Heaviside Function is known as the function that can mathematically describe the switching process in engineering applications. We often encounter some functions whose values change abruptly at specified units of time t. The value of t = 0 is taken as an appropriate time to switch on or off a given voltage.


Unit Step Function Examples

Some unit step function examples are switching on and off of voltage, binary cellular responses to chemical signals, etc.


Properties of Step Function

Some of the most important properties of Step functions are as follows:

  • The product or sum of two-step functions will also result in a step function.

  • The piecewise linear function is the definite integral of a step function.

  • If a number is multiplied by a step function then the product is also a step function. This is an indication that step functions create algebra over real numbers.

We can observe step-functions when dealing with other types of functions for different reasons. For instance, a trivial example of a step function is a constant function. The simplest non-constant step function is sign function “sgn(x)”, because this function results -1 for the negative inputs and 1 (i.e. +1) for the positive input values. Other types include the Heaviside function and rectangular function, etc.


Domain and Range of Step Function

In the case of a step function, for each value of x, f(x) takes the value of the greatest integer, less than or equal to x. For example:

(-2.19) = -3

(3.67) = 3

(-0.83) = -1

The domain of this function is a group of real numbers that are divided into intervals such as (-5, 3), (-4, 2), (-3, 1), (-2, 0), and so on. This helps us to explain the domain and range of a step function. Below we have generalized

(x) = -2, -2 ≤ x < -1

(x) = -1, -1 ≤ x < 0

(x) = 0, 0 ≤ x < 1

(x) = 1, 1 ≤ x < 2


Step Function Graph

The method of drawing a step function graph is similar to that of any piecewise function. In this graphing method, we have to graph each part of the function individually. The following steps are to be followed while drawing a step graph:

  • In the first step, we have to draw a horizontal line segment at each constant output value through input values to which it corresponds.

  • In the second step, we have to draw a closed filled-in circle or a closed circle point at the induced endpoint on each horizontal line. This means that if the end value is included in that particular interval then it has to be denoted with a filled-in circle.

  • In the final step, we have to draw an open circle at the endpoint that is excluded from each horizontal line. If the end value is not included in this particular interval then it should be denoted with an open circle.


The graph of a step function is given below:


(Image will be uploaded soon)


Step Function Examples

Draw a graph for the following step function

\[ f(x) = \left\{\begin{matrix} -2, x < 1 & \\  0, -1 \leq x \leq 2 & \\  2, x > 1 & \end{matrix}\right.\]

Solution: From the given data we have, -2, 0, 2 are the respective values of y.

x < -1 which means that the values of x can be x = …. -4, -3, -2, -1.

-1 < x < 2 or -1 = x or x = 2, so the values of x = -1, 0, 1, 2

x > 1 means the value of x can be x= 1, 2, 3, 4, 5…


(Image will be uploaded soon)


By plotting the above values on graph paper, the following graph can be obtained. The graph gives a picture of a group of steps and so it is known as a Step Function Graph. The left-hand side endpoint is a dark dot in order to show that the point is part of the graph while the right-hand side endpoint is an arrow denoting that the values are infinite. Hence, only the dark dots refer to finite definite values.

FAQs on What is Step Function?

1. What is the Step Function Definition?

A step function may be defined as a constant function that has only a finite number of pieces. In mathematics, a step function refers to a finite linear combination of indicator functions of given intervals. Step Function is also known as the Greatest Integer Function or Floor Function. We can also come in contact with step functions while dealing with other types of functions. For example, sign function “sgn(x)”, Heaviside Function, and Rectangular function etc. Step Function is used to coordinate session-based applications. For example, it can be used to coordinate all the steps of a checkout process on an e-commerce site.

2. What is the Step Signal Definition? What are the Properties of the Step Function?

Step signal also known as step function is defined as a constant function that has only a finite number of pieces. In mathematics, a step function refers to a finite linear combination of indicator functions of given intervals.


Some of the most important properties of Step functions are as follows:

  • The product or sum of two-step functions will also result in a step function.

  • It can only take a finite number of values.

  • The piecewise linear function is the definite integral of a step function.

  • If a number is multiplied to a step function then the product is also a step function. This is an indication that step functions create algebra over real numbers.

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