Dot Product of Vectors in R Programming

Last Updated : 25 Aug, 2020

In mathematics, the dot product or also known as the scalar product is an algebraic operation that takes two equal-length sequences of numbers and returns a single number. Let us given two vectors A and B, and we have to find the dot product of two vectors.

Given that,

$A = a_1i + a_2j + a_3k$

and,

$B = b_1i + b_2j + b_3k$

where,
i: the unit vector along the x directions
j: the unit vector along the y directions
k: the unit vector along the z directions

Then the dot product is calculated as:

$DotProduct = a_1 * b_1 + a_2 * b_2 + a_3 * b_3$

Example:

Given two vectors A and B as,

A = 3i + 5j + 4k,
and
B = 2i + 7j + 5k
Dot Product = 3 * 2 + 5 * 7 + 4 * 5 = 6 + 35 + 20 + 61

Computing Dot Product in R

R language provides a very efficient method to calculate the dot product of two vectors. By using dot() method which is available in the geometry library one can do so.

Syntax: dot(x, y, d = NULL)
Parameters:
x: Matrix of vectors
y: Matrix of vectors
d: Dimension along which to calculate the dot product
Return: Vector with length of dth dimension

Example 1:

R

# R Program illustrating
# dot product of two vectors
  
# Import the required library
library(geometry)
  
# Taking two scalar values
a = 5
b = 7
  
# Calculating dot product using dot()
print(dot(a, b, d = TRUE))

Output:

[1] 35

Example 2:

R

# R Program illustrating
# dot product of two vectors
  
# Import the required library
library(geometry)
  
# Taking two complex values
a = 3 + 1i
b = 7 + 6i
  
# Calculating dot product using dot()
print(dot(a, b, d = TRUE))

Output:

[1] 15+25i

Example 3:

R

# R Program illustrating
# dot product of two vectors
  
# Import the required library
library(geometry)
  
# Taking two simple vectors
a = c(1, 4)
b = c(7, 4)
  
# Calculating dot product using dot()
print(dot(a, b, d = TRUE))

Output:

[1] 23

Example 4:

In this following example let’s take two 2D arrays and calculate the dot product of these two. To create a 2D array in R please refer Multidimensional Array in R.

R

# R Program illustrating
# dot product of two vectors
  
# Import the required library
library(geometry)
  
# Taking two 2D array
vector1 = c(2, 1)
vector2 = c(0, 3)
a = array(c(vector1, vector2), dim = c(2, 2))
vector1 = c(4, 2)
vector2 = c(9, 3)
b = array(c(vector1, vector2), dim = c(2, 2))
  
# Calculating dot product using dot()
print(dot(a, b, d = TRUE))

Output:

[1] 10  9

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