Question

Write the following Python script:

Imagine you live in a world without modules in Python! No numpy! No scipy! Write a Python script that defines a function called mat_mult() that takes two lists of lists as parameters and, when possible, returns a list of lists representing the matrix product of the two inputs. Your function should make sure the lists are of the appropriate size first - if not, your program should print “Invalid sizes” and return None. Note: it is actually tricky to make a useful list of zeros. For instance, if you need to start with a 5 row, 6 column double list of 0, you might be tempted to try:

'''

thing = [ [ 0 ] ∗ 6 ] ∗ 5

'''

and if you look at it in the console window, it would appear to be a 5 by 6 list of lists containing all zeros! However - try the following and see what happens:

'''

thing [ 2 ] [ 5 ]

thing

'''

Notice that the item in index 5 of every row has changed, not just the row with index 2! Given the difficulty, I will give you the line of code that will create a list of lists that is num_rows by num_cols:

'''

ans = [ [ 0 for col in range ( num_cols ) ] for row in range ( num_rows ) ]

'''

• The autograder will not allow numpy (or anything else!) to be imported
• Your solution will likely have a triple loop. Do some matrix multiplications by hand for small and then larger matrices and figure out what processes you are using. Code those.
• Given that your solution will likely have a triple loop, be careful with your indentation!
• As noted, trying to create an empty list of list of 0 can be problematic since the interior lists are actually pointing to the same information.

Answer 1

def multiplyMatrix(A,row1, col1, B, row2, col2): 
                          
    # Matrix to store the result  
    C = [[0 for i in range(MAX)] for j in range(MAX)] 
  
    # Checking if the multiplication is Possible or not 
    if (row2 != col1) : 
        print("Invalid Sizes") 
        return None
      
    # Multiplying  
    for i in range(row1) : 
        for j in range(col2) : 
            C[i][j] = 0
            for k in range(row2) : 
                C[i][j] += A[i][k] * B[k][j];  
  
    print("Resultant Matrix(AxB): ") 
    for i in range(row1) :  
        for j in range(col2) :  
            print(C[i][j], end = " ") 
  
        print() 
  
MAX = 1000  
A = [[0 for i in range(MAX)] for j in range(MAX)] 
B = [[0 for i in range(MAX)] for j in range(MAX)]

row1 = int(input("Enter the number of rows of First Matrix: ")) 
col1 = int(input("Enter the number of columns of First Matrix: ")) 
print("Enter the elements of First Matrix: ");  
for i in range(row1) :  
    for j in range(col1) :  
        A[i][j] = int(input()) 
  
row2 = int(input("Enter the number of rows of Second Matrix: "))  
col2 = int(input("Enter the number of columns of Second Matrix: "))  
  
print("Enter the elements of Second Matrix: ");  
for i in range(row2) :  
    for j in range(col2) : 
        B[i][j] = int(input()) 

print("A: ") 
for i in range(row1) :  
    for j in range(col1) :  
        print(A[i][j], end = " ") 
  
    print()
    
print("B: ") 
for i in range(row2) :  
    for j in range(col2) :  
        print(B[i][j], end = " ") 
  
    print()
multiplyMatrix(A, row1, col1, B, row2, col2)