matrix multiplication in python code example

Example 1: matrix multiplication in python

# Program to multiply two matrices using nested loops

# 3x3 matrix
X = [[12,7,3],
    [4 ,5,6],
    [7 ,8,9]]
# 3x4 matrix
Y = [[5,8,1,2],
    [6,7,3,0],
    [4,5,9,1]]
# result is 3x4
result = [[0,0,0,0],
         [0,0,0,0],
         [0,0,0,0]]

# iterate through rows of X
for i in range(len(X)):
   # iterate through columns of Y
   for j in range(len(Y[0])):
       # iterate through rows of Y
       for k in range(len(Y)):
           result[i][j] += X[i][k] * Y[k][j]

for r in result:
   print(r)

Example 2: matrix multiplication python

# Program to multiply two matrices using nested loops

# 3x3 matrix
X = [[12,7,3],
    [4 ,5,6],
    [7 ,8,9]]
# 3x4 matrix
Y = [[5,8,1,2],
    [6,7,3,0],
    [4,5,9,1]]
# result is 3x4
result = [[0,0,0,0],
         [0,0,0,0],
         [0,0,0,0]]

# iterate through rows of X
for i in range(len(X)):
   # iterate through columns of Y
   for j in range(len(Y[0])):
       # iterate through rows of Y
       for k in range(len(Y)):
           result[i][j] += X[i][k] * Y[k][j]

for r in result:
   print(r)

Example 3: matrix multiplication in python

# input two matrices of size n x m 
matrix1 = [[12,7,3], 
        [4 ,5,6], 
        [7 ,8,9]] 
matrix2 = [[5,8,1], 
        [6,7,3], 
        [4,5,9]] 
  
res = [[0 for x in range(3)] for y in range(3)]  
  
# explicit for loops 
for i in range(len(matrix1)): 
    for j in range(len(matrix2[0])): 
        for k in range(len(matrix2)): 
  
            # resulted matrix 
            res[i][j] += matrix1[i][k] * matrix2[k][j] 
  
print (res)

Example 4: python matrix multiplication

>>> a = np.array([[ 5, 1 ,3], 
                  [ 1, 1 ,1], 
                  [ 1, 2 ,1]])
>>> b = np.array([1, 2, 3])
>>> print a.dot(b)
array([16, 6, 8])