Courses
Courses for Kids
Free study material
Free LIVE classes
More

Difference Between Onto and Into Functions

ffImage
hightlight icon
highlight icon
highlight icon
share icon
copy icon
LIVE
Join Vedantu’s FREE Mastercalss

What are Onto and Into Functions: Introduction

To explain the Onto and Into functions:  In mathematics, a function is a relationship between a set of inputs, called the domain, and a set of outputs, called the range or codomain. It associates each input with exactly one output. Functions are often denoted by symbols such as f(x) or g(x). Understanding Onto and Into functions is crucial in various areas of mathematics, such as algebra, analysis, and set theory. They also have practical applications in fields like computer science, cryptography, and data analysis, where the mapping of elements and ensuring coverage are important considerations. Now, let's explore the concepts of Onto and Into functions:


Defining Onto Functions

A function is called an Onto function if, for every possible output value in the range, there is at least one corresponding input value in the domain that produces that output. No element in the range is left unmapped by the function. Here are some key points to understand about Onto functions:


  • Coverage of the Range or Surjectivity: Onto functions are often referred to as surjective functions because they establish a surjection, which is a mapping that covers the entire range. It means that for every element in the range, there exists at least one element in the domain that maps to it. The function doesn't miss or skip any values in the range.

  • Multiple Inputs for a Single Output: It is possible for an Onto function to have multiple inputs producing the same output value.

  • Unmapped Elements: In an Onto function, no elements in the range are left unmapped. Each and every element in the range is associated with at least one element in the domain.

  • Existence of Pre-Images: For every element in the range, there exists at least one element in the domain that maps to it. These elements in the domain, which map to a specific element in the range, are called pre-images.

  • Visual Representation: In graphical representations, an Onto function is illustrated by ensuring that every point in the range has at least one arrow pointing to it. This demonstrates that every element in the range is covered by the function.

  • Number of Onto functions: If A and B are two sets having m and n elements respectively, such that  $1\leq n\leq m$ , then the number of Onto functions from A to B can be given by,

$\sum_{r=1}^{n}{(-1)^{n-r}}{^{n}\textrm{C}_r}r^{m}$ .


Defining Into Functions

A function is called an Into function if there exists at least one element in the codomain of the function, which does not  have a pre-image in the domain of the function. In other words, a function is an onto function if it is not an onto function. Hence, the range and codomain of an Into function are not same, but the range of an Into function is surely a subset of the codomain of the function. Here are some key points to understand about Onto functions:


  • Partial Coverage: Into functions may still map some elements in the range to elements in the domain, but they do not achieve complete coverage. Certain output values have no pre-image or corresponding input.

  • Multiple Outputs for a Single Input: In Into functions, it is possible for different inputs from the domain to produce the same output value. This means that some elements in the range may have multiple pre-images.

  • Restriction of the Range: Into functions can also be seen as functions with a restricted range. The range of the function is a subset of the total possible values, excluding some elements that are not mapped.

  • Visual Representation: In graphical representations, Into functions are illustrated by having some points in the range without arrows pointing to them. This indicates the absence of a mapping for those elements.


Difference between Onto and Into Functions

S. No

Category

Onto Function

Into Function

1

Surjectivity

Onto functions are subjective in nature, which means for every element in the range, there exists at least one element in the domain that maps to it.

A function is called an Into function if there exists at least one element in the codomain of the function, which does not  have a pre-image in the domain of the function.

2

Unmapped Elements

In an Onto function, no elements in the range are left unmapped. Each element in the range is associated with at least one element in the domain.

In an Into function, at least one element in the range is left unmapped.

3

Visual Representation

An Onto function is illustrated by ensuring that every point in the range has at least one arrow pointing to it. This demonstrates that every element in the range is covered by the function.

Into functions are illustrated by having some points in the range without arrows pointing to them. This indicates the absence of a mapping for those elements.

4

Coverage of the Range

The range and codomain of an Onto function are the same.

The range and codomain of an Into function are not same, but the range of an Into function is surely a subset of the codomain of the function.

5

Number of Functions

If A and B are two sets having m and n elements respectively, such that  $1\leq n\leq m$ , then the number of Onto functions from A to B can be given by,

$\sum_{r=1}^{n}{(-1)^{n-r}}{^{n}\textrm{C}_r}r^{m}$ .

There is no way to know the number of Into functions, which can be possible between two given sets.


Summary

We come to the conclusion in this article that there are difference between the Into and Onto functions. The input set (domain) for Onto functions should be connected to each member of the output set (codomain). On the other hand, for Into functions, the output set (codomain) must contain at least one element that is not linked to the input set (domain). The codomain and range of an onto function are the same. For Into function, the range is surely a subset of the codomain.

Last updated date: 26th Sep 2023
Total views: 2.7k
Views today: 0.02k
Competitive Exams after 12th Science

FAQs on Difference Between Onto and Into Functions

1. Are the range and codomain of an Into function the same?

No. The range and codomain of an Into function are not same, but the range of an Into function is surely a subset of the codomain of the function.

2. How to know whether a function is an Onto function or not?

If the range of a given function is equal to the codomain of the function, then it can be concluded that the given function is an Onto function. Otherwise, the function is Into function.

3. How to find the number of possible Onto functions between two given sets?

If A and B are two sets having m and n elements respectively, such that  $1\leq n\leq m$ , then the number of Onto functions from A to B can be given by,

$\sum_{r=1}^{n}{(-1)^{n-r}}{^{n}\textrm{C}_r}r^{m}$ .

4. Can an onto function have multiple inputs producing the same output?

Yes, an onto function can have multiple inputs producing the same output. It is possible for different elements in the domain to map to the same element in the range. The requirement is that every element in the range has at least one corresponding input.

5. Can a function be both Onto and Into?

No. If a function is an Onto function, then the function is not an Into function. The inverse is also the same.