Python Program to Add 2 Matrices

Problem: Write a program in python to add two matrices.

Example:

m1    = [[1,2],
         [8,1]]

m2    = [[1,1],
         [1,1]]

m1+m2 = [[2,3],
         [9,2]]

In python, we can easily represent a matrix using a nested list.

For example, m1 = [[1,2],[8,1]] is a list in which each element itself is a list.

Each row in a matrix can be denoted by m1[i] and the element in the i^th row and j^th column as m1[i][j].

So using a nested for loop we can easily add elements of the first matrix to their corresponding element of the second matrix.

Method 1: Matrix Addition Using Nested For Loop

#Matrix I
m1    = [[1,2],
         [8,1]]

#Matrix II 
m2    = [[1,1],
         [1,1]]
  
#Initialize resultant matrix with 0       
res   = [[0,0], 
         [0,0]]
         
for i in range(len(m1)):
    for j in range(len(m1[0])):
        res[i][j] = m1[i][j] + m2[i][j]
        
print(res)

Output:

[[2, 3], [9, 2]]

In the above program, we have used len(m1) to find the number of rows and len(m1[0]) to find the number of columns in the matrix m1.

Method 2: Matrix Addition using List Comprehension

In this method instead of using a nested for loop, we will use list comprehension to add matrices.

I highly recommend you to read our list comprehension tutorial if you don’t know what it is?

#Matrix I
m1    = [[1,2],
         [8,1]]

#Matrix II 
m2    = [[1,1],
         [1,1]]
         
         
res = [[m1[i][j] + m2[i][j] for j in range(len(m1[0]))] for i in range(len(m1))]   
print(res)

Output:

[[2, 3, 2], [9, 2, 3]]