chapter 16

Matrix multiplication by using dot() function

For a given two ndarrays a,b, if we perform a*b ==> element level multiplication will be happened.

To perform matrix level multiplication we have to use dot() function.

dot() function in available in numpy module.

dot() method is present in ndarray class also.

Example

Python

# dot() function in numpy module
import numpy as np
help(np.dot)

Output

PowerShell

Help on function dot in module numpy:

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

Example

Python

# dot() method in ndarray class
help(np.ndarray.dot)

Output

PowerShell

Help on method_descriptor:

dot(...)
    a.dot(b, out=None)
    
    Dot product of two arrays.

figar banana

Example

Python

# Element level multiplication
a = np.array([[10,20],[30,40]])
b = np.array([[1,2],[3,4]])
print(f"array a : \n {a}")
print(f"array b : \n {b}")
print("Element level multiplication ")
ele_multiplication = a* b
print(f"array b : \n {ele_multiplication}")

Output

PowerShell

array a :
 [[10 20]
 [30 40]]
array b :
 [[1 2]
 [3 4]]
Element level multiplication
array b :
 [[ 10 40]
 [ 90 160]]

Figar banana

Example

Python

# matrix multiplication using dot() function in numpy module
a = np.array([[10,20],[30,40]])
b = np.array([[1,2],[3,4]])
dot_product = np.dot(a,b)
print(f"array a : \n {a}")
print(f"array b : \n {b}")
print(f"Matrix multiplication:\n {dot_product} ")

Output

PowerShell

array a :
 [[10 20]
 [30 40]]
array b :
 [[1 2]
 [3 4]]
Matrix multiplication:
 [[ 70 100]
 [150 220]]

Example

Python

# matrix multiplication using dot() method in ndarray class
a = np.array([[10,20],[30,40]])
b = np.array([[1,2],[3,4]])

Output

PowerShell

output nhi h

Example

Python

dot_product = a.dot(b)
print(f"array a : \n {a}")
print(f"array b : \n {b}")
print(f"Matrix multiplication:\n {dot_product} ")

Output

PowerShell

array a :
 [[10 20]
 [30 40]]
array b :
 [[1 2]
 [3 4]]
Matrix multiplication:
 [[ 70 100]
 [150 220]]