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Nikita Parmar

Updated on 25th September, 2023 , 5 min read

Signum Function: Definitions, Examples, Properties, Domain, Graph, and Applications

Signum Function Overview

The Signum Function is a useful function in mathematics that allows us to determine the sign of a real number. It is commonly written as a function of a variable and is denoted by f (x) or sgn (x). It is also possible to write it as a sgn (x). Signum Function also has applications in physics, electronics, and artificial intelligence, making it even more crucial to understand it. A signum function is neither a one-one nor an onto function since different components have the same image and a pre-image has different pictures in the co-domain and domain set. 

What is the Signum Function?

The Signum function aids in determining the sign of the real value function, with attributes +1 (positive 1) for positive input values and attributes -1 (negative 1) for negative input values. The signum function has many applications in physicsengineering, and mathematics, and it is widely used in artificial intelligence for forecasting. The sign function, also known as the signum function (from signum, Latin for "sign"), is a mathematical function that yields the sign of a real integer. The sign function is frequently expressed in mathematical notation as sgn (x).

Signum Function

Examples of Signum Function

What would the signum function produce for the values of x? (x = {- 4.93, - 7.66, 12, 0, 4.2, 2.33333, -8.10})?

Solution: For the input values of x, we use the signum function to obtain the output.

 = {- 4.93, - 7.66, 12, 0, 4.2, 2.33333, -8.10}

Result = -1,-1,+1,0,+1,+1,-1

Properties of the Signum Function

The signum function sgn(x) has the following characteristics-

  1. If sgn(x) = 1, x>0
  2. If sgn(x) = -1, x<0
  3. x = |x|sgn(x)
  4. sgn(x.y) = sgn(x).sgn(y)
  5. sgn(sgn(x)) = sgn(x)
  6. sgn(x+y) < sgn(x) + sgn(y) + 1
  7. If x≠0, then sgn(x)sgn(1/x) = 1
  8. If x≠0, then sgn(1/x) = 1/sgn(x)
  9. sgn(x)+sgn(y)-1 ≤ sgn(x+y)
  10. If x≠0, then sgn(x)=sgn(1/x)
  11. If y≠0, then sgn(x/y)=sgn(x)/sgn(y)

Signum Function

Domain and Range of Signum Function

The domain of the signum function encompasses all real numbers and is depicted on the x-axis, whereas the range of the signum function has just two values, +1 and -1, and is shown on the y-axis.

  1. Domain = R
  2. Range = {-1, 0, 1}

Signum Function

Graph of Signum Function

The signum function graph contains two horizontal lines parallel to the x-axis. Part of the line in the first quadrant is parallel to the positive x-axis and reflects the outputs of all positive x-values. In the third quadrant, a portion of the line is parallel to the negative x-axis and reflects the output of the negative x-values. A signum function's domain contains all real numbers and is depicted along the x-axis, but its range has just two values, +1 and -1, and is displayed on the y-axis.

Signum Function

Signum Function for Real Numbers

The signum function is also known as the absolute value function's derivative. As a result, each real number has the potential to be expressed as the product of its absolute value. As an example,

x = sgn(x).|x|

As a result, if x is not equal to zero, then

sgn(x) = x/|x|

Signum Function for Complex Arguments

The signum function of any complex number is defined as follows-

Let's call the complex number 'a'.


If an is equal to zero, then

sgn(a) = 0

If an is greater than zero, then

sgn(a) = a/|a|

As a result, for a = 0, sgn(a) is the projection of an onto a unit circle as follows-

a ∈ C| |a| = 1

As a result, given real inputs, the complex signum function tends to reduce itself to the real signum function, yielding:

a sgna- = |a| 

where a- denotes a's complex conjugate.

Applications of Signum Function

The Signum function has several uses in diverse disciplines. Some of its uses include-

  1. It is beneficial to project a complicated number onto the unit circle.
  2. It is used to determine the sign of a real number.
  3. It is also utilized in electrical gadgets to implement the on/off switch.
  4. It may also be used in thermostats to start cooling beyond a certain temperature and cease cooling below a certain temperature.
  5. It may also be used to forecast the likelihood of an event occurring.
  6. When the signum function is integrated, a positively or negatively inclined line with the X-axis is formed.

Important things to learn about Signum Function

function is a relationship that connects every input element to exactly one output component. A function connects the inputs and outputs. The following are some of the important things to learn about the signum function lessons from the topic-

  1. Output: The output of a function is the result or response.
  2. The range is the sum of all the outputs.
  3. Relation: A relation is a relationship between numbers/symbols/characters from one set and numbers from another set.
  4. A function drives items from the domain set and connects them to elements from the codomain set.
  5. Dependent Variable: The dependent variable in a function is the one whose value is determined by one or more independent variables of the specified function.
  6. Independent Variable: An independent variable in a function is one whose value is unrelated to any other variable.
  7. Graph: A data-illustrated figure that explains the relationship between two or more values, dimensions, or characters.
  8. A relation is assumed to be a function if each element in set A has exactly one image in set B.


Calculus, being a key building component in mathematics, is strongly reliant on functions. The nature of the functions distinguishes them from other sorts of links. In mathematics, a function is defined as a collection of rules that individually provide a unique outcome for all input x. The formulation of a function in mathematics frequently requires the use of mapping or transformation. Functions are often denoted by alphabets such as t, 9, and h. The signum function can be used to help determine the sign of the real value function. It assigns the value +1 (positive 1) to the function's positive input values and the value -1 (negative 1) to the function's negative input values. The signum function is employed in many fields, including physics, engineering, and mathematics. It is also widely used in artificial intelligence, mainly predicting.

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Frequently Asked Questions

Is the signum function a straight line?

Ans. Yes, it is linear when the system reaches a steady state, but I need a linear model of this system when given a unit Step input, which would cause the signum function to become severely non-linear.

Is it possible to write the Signum Function as an invertible function?

Ans. The signum function cannot be inverted. The inverse function's -1 or +1 inputs cannot result in the primary signum function's initial input of x being returned.

What exactly is the signum function?

Ans. The Signum function aids in determining the sign of the real value function, with attributes +1 (positive 1) for positive input values and attributes -1 (negative 1) for negative input values.

What are the uses of the signum function?

Ans. The signum function has many applications in physics, engineering, and mathematics, and it is widely used in artificial intelligence for forecasting.

What is the Signum Function's Range?

Ans. The signum function's range is limited to the three numbers -1, 0 and +1. The range of all the distinct input values of x in the signum function of f(x) is simply -1, 0, and +1. Signum Function Range = -1, 0, +1.

Is the Signum Function an Even or an Odd Function?

Ans. The signum function is odd since sgn(x) = -sgn(-x).

What is a Signum Function's Domain?

Ans. A signum function's domain contains all real number values. The signum function accepts both positive and negative numbers as inputs.

What is the Difference Between the Signum and Sine Functions?

Ans. The distinction between a signum function and a sine function can be illustrated visually. A signum function's graph is a line parallel to the x-axis on each side of the origin, whereas a sine function's graph is a waveform passing through the origin. The signum function and sine function both share the same domain of real numbers, but the signum function's range is either -1 or +1, whereas the sine function's range is between -1 and +1.

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