Python program to add two matrices

Prerequisite : Arrays in Python, Loops, List Comprehension Program to compute the sum of two matrices and then print it in Python. We can perform matrix addition in various ways in Python. Here are a two of them. Examples:

Input :
 X= [[1,2,3],
    [4 ,5,6],
    [7 ,8,9]]
 
Y = [[9,8,7],
    [6,5,4],
    [3,2,1]]
 
Output :
 result= [[10,10,10],
         [10,10,10],
         [10,10,10]]

Using Nested Loops

Python

# Program to add two matrices using nested loop

X = [[1,2,3],
    [4 ,5,6],
    [7 ,8,9]]

Y = [[9,8,7],
    [6,5,4],
    [3,2,1]]


result = [[0,0,0],
         [0,0,0],
         [0,0,0]]

# iterate through rows
for i in range(len(X)):

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

for r in result:
     print(r)

Output:

[10, 10, 10]
[10, 10, 10]
[10, 10, 10]

Time Complexity: O(N²), as we are traversing the matrix using nested loops.

Auxiliary Space: O(N*N), as we are using an extra space result matrix.

Explanation :- In this program we have used nested for loops to iterate through each row and each column. At each point we add the corresponding elements in the two matrices and store it in the result.

Using nested list comprehension

Here is another approach for addition of two matrix addition using nested list comprehension. 

Python

# Program to add two matrices
# using list comprehension

X = [[1,2,3],
    [4 ,5,6],
    [7 ,8,9]]

Y = [[9,8,7],
    [6,5,4],
    [3,2,1]]

result = [[X[i][j] + Y[i][j]  for j in range(len(X[0]))] for i in range(len(X))]

for r in result:
    print(r)

Output:

[10, 10, 10]
[10, 10, 10]
[10, 10, 10]

Explanation:- The output of this program is the same as above. We have used nested list comprehension to iterate through each element in the matrix.

Time Complexity: O(N²), as we are traversing the matrix using nested loops.

Auxiliary Space: O(N*N), as we are using an extra space result matrix.