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  1. Prepare
  2. Python
  3. Numpy
  4. Dot and Cross
  5. Discussions

Dot and Cross

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  • rohitambasta_ii1
     + 0 comments

    Using Built-ins:

    import numpy as np
N= int(input())

A = [list(map(int, input().split())) for i in range(N)]
B = [list(map(int, input().split())) for i in range(N)]

print(np.matmul(A, B))

    Without Using built-ins

    import numpy as np
N= int(input())

A = [list(map(int, input().split())) for i in range(N)]
B = [list(map(int, input().split())) for i in range(N)]



final_array =[]

for i in range(N):
    sum_total= []
    for j in range(N):
        sum =0
        for k in range(N):
            sum = sum + (A[i][k] * B[k][j])
        sum_total.append(sum)
     
    final_array.append(sum_total)
print(np.array(final_array))    
           
# For Your Understanding
# ------------------------------

# print(A)  #[['1', '2'], ['3', '4']]
# print(B)  #[['1', '2'], ['3', '4']]  

        #    i, j, k= 0, 0, 0   1 * 1 = 1
        #    i, j, k= 0, 0, 1   2 * 3 = 6
        #    i, j, k= 0, 1, 0   1 * 2 = 2
        #    i, j, k= 0, 1, 1   2 * 4 = 8
        #    i, j, k= 1, 0, 0   3 * 1 = 3
        #    i, j, k= 1, 0, 1   4 * 3 = 12
        #    i, j, k= 1, 1, 0   3 * 2 = 6
        #    i, j, k= 1, 1, 1   4 * 4 = 16
    

# (i[0][0]*j[0][0]) +  (i[0][1]*j[1][0])      (i[0][0]*j[0][1]) + (i[0][1]*j[1][1])   .............


# Ex- Matrix A & B
# [[1 2]       [[1 2]
#  [3 4]]       [3 4]]

# Product of A & B
# (1*1) + (2*3)         (1*2) + (2*4)
# (3*1) + (4*3)         (3*2) + (4*4)

# Result of above Matrix Multiplication
# 7                      10
# 15                     22

  • yashdeora98294
     + 0 comments

    Here is HackerRank Dot and Cross in Python solution - https://programmingoneonone.com/hackerrank-dot-and-cross-problem-solution-in-python.html

  • daturpinusn
     + 0 comments

    Not sure why they want you to do dot and cross when numpy has a matrix multiplication method.

    print(np.matmul(a, b))

  • arohi_agrawal111
     + 0 comments
    import numpy as np

N = int(input())

A = np.array([list(map(int, input().split())) for _ in range(N)])
B = np.array([list(map(int, input().split())) for _ in range(N)])

print(np.matmul(A, B))

  • fa_caviglia
     + 1 comment
    import numpy as np

n = int(input())

a = np.array([list(map(int, input().split())) for _ in range(n)])
b = np.array([list(map(int, input().split())) for _ in range(n)])

matrix = np.zeros((n, n), dtype = int)
for i in range(n):
    for j in range(n):
        matrix[i, j] = np.sum([a[i, k] * b[k, j] for k in range(n)])
    
print(matrix)