# np.dot function – Python NumPy dot() Function

NumPy dot() Function:

np.dot function: The dot() method in the NumPy module is used to do the dot product of two arrays. Specifically,

• It is the inner product of vectors if both a and b are 1-D arrays (without complex conjugation).
• Matrix multiplication is used when both a and b are 2-D arrays, however, matmul or a @ b is preferred.
• If either a or b is 0-D (scalar), it is equivalent to multiply and using numpy.multiply(a, b) or a * b is preferred.
• It is a sum product over the last axis of a and b if “a” is an N-D array and “b” is a 1-D array.
• It is a sum product over the final axis of a and the second-to-last axis of b if “a” is an N-D array and “b” is an M-D array (where M>=2).
dot(a, b)[i, j, k, m] = sum(a[i, j, :] * b[k, : ,m])

Syntax:

numpy.dot(a, b, out=None)

Parameters

a: This is required. It is the first array_like parameter given as input.

b: This is required. It is the second array_like parameter given as input.

out: This is optional. It is the location where the result will be stored.

Return Value:

.dot() python: The dot product of a and b is returned. A scalar is returned if a and b are both scalars or both 1-D arrays; otherwise, an array is returned. If out is specified, it will be returned.

Note: If the last dimension of is not the same size as the second-to-last dimension of b, the ValueError exception is thrown.

## NumPy dot() Function in Python

Example1

Approach:

• Import numpy module using the import keyword.
• Pass two random numbers as the arguments to the dot() function of numpy module to calculate the dot product of the given two numbers.
• Store it in a variable.
• Print the dot product of the given two numbers.
• The Exit of the Program.

Below is the implementation:

# Import numpy module using the import keyword
import numpy as np
# Pass two random numbers as the arguments to the dot() function
# of numpy module to calculate the dot product of given two numbers
# Store it in a variable.
rslt = np.dot(4, 6)
# Print the dot product of the given two numbers
print("The dot product of given two numbers = ", rslt)

Output:

The dot product of given two numbers = 24

Example2

Approach:

• Import numpy module using the import keyword.
• Give the first array as static input and store it in a variable.
• Give the second array as static input and store it in another variable.
• Pass the given two array’s as an argument to the dot() function of numpy module to get the inner dot product of the given two arrays.
• Store it in another variable.
• Print the inner dot product of the given two arrays.
• The Exit of the Program.

Below is the implementation:

# Import numpy module using the import keyword
import numpy as np
# Give the first array as static input and store it in a variable.
fst_arry = [4, 9, 2]
# Give the second array as static input and store it in another variable.
scnd_arry = [6, 3, 5]
# Pass the given two array's as an argument to the dot() function of numpy module
# to get the inner dot product of the given two arrays.
# Store it in another variable.
rslt = np.dot(fst_arry, scnd_arry)
# Print the inner dot product of the given two arrays.
print("The inner dot product of the given two arrays = ", rslt)

Output:

The inner dot product of the given two arrays = 61

Example3

Numpy dot function: Here dot() function is used to calculate the dot product for the complex numbers

# Import numpy module using the import keyword
import numpy as np
# Pass the random list of complex numbers as an argument to the array() function
# to create an array.
# Store it in a variable.
fst_arry = np.array([2+4j, 1+3j])
# Pass the random list of complex numbers as an argument to the array() function
# to create another array.
# Store it in another variable.
scnd_arry = np.array([1+2j, 3+2j])
# Pass the given two array's as the argument to the dot() function of numpy module
# to get the dot product of the given two arrays of complex numbers.
# Store it in another variable.
rslt = np.dot(fst_arry, scnd_arry)
# Print the dot product of the given two arrays of complex numbers.
print("The dot product of the given two arrays of complex numbers = ")
print(rslt)


Output:

The dot product of the given two arrays of complex numbers =
(-9+19j)

Example4

Dot function python: Here dot() function is used to calculate the dot product for the 2D arrays i.e matrix.

The dot() function returns matrix multiplication when two matrices are given.

# Import numpy module using the import keyword
import numpy as np
# Pass the random list(2D) as an argument to the array() function
# to create an array.
# Store it in a variable.
fst_arry = np.array([[5, 6],
[1, 7]])
# Pass the random list(2D) as an argument to the array() function
# to create another array.
# Store it in another variable.
scnd_arry = np.array([[2, 4],
[8, 7]])
# Pass the given two array's as the argument to the dot() function of numpy module
# to get the dot product of the given two 2D arrays
# Here it returns the matrix multiplcation of given arrays(matrices)
# Store it in another variable.
rslt = np.dot(fst_arry, scnd_arry)
# Print the matrix multiplcation of given two arrays(matrices)
print("The matrix multiplcation of given two arrays(matrices) = ")
print(rslt)


Output:

The matrix multiplcation of given two arrays(matrices) =
[[58 62]
[58 53]]