Algorithm for finding the dot product of 2 arrays written in Python for MIT Open Learning Library on Machine Learning (MITx - 6.036)

Dot Product Algorithm.py

# Written by SigmaTech
# Beat a Computer Science graduate at desigining this algorithm at the same start time

# Make sure that the columns of M1 match the rows of M2
# Create an answer array M3
# For each entry (array) of M1, 

def getRowsColumns(V):
    return (len(V), len(V[0]))

def array_mult(A, B):

    finalAnswer = []
    
    # Store the number of columns and rows for the results
    resultRows = getRowsColumns(A)[0]
    resultColumns = getRowsColumns(B)[1]
    
    #print("Dimensions of A", getRowsColumns(A))
    #print("Dimensions of B", getRowsColumns(B))
    #print("Dimensions of result:", (resultRows, resultColumns))
    
    # Make sure that the columns of A match the rows of B
    dim_A = getRowsColumns(A)
    dim_B = getRowsColumns(B)
    if dim_A[1] != dim_B[0]:
        return None
        
    # Create our blank answer
    C = []
    
    for currentRow in range(resultRows):
        newRowToAppendToAnswer = []
        
        for currentColumn in range(resultColumns):
            # Sum up all the products for the corresponding entries in each array
            sum = 0
            
            # For every entry in A[currentRow], multiply by B[currentColumn][currentRow] and add to sum
            for A_column, entry in enumerate(A[currentRow]):
                product = entry * (B[A_column][currentColumn])
                sum = sum + product
                print("Multiplying", entry, "by", (B[A_column][currentColumn]), "=", product)
                
            newRowToAppendToAnswer.append(sum)
            print("For row", currentRow, "column", currentColumn, "we got", sum)
            
        finalAnswer.append(newRowToAppendToAnswer)
    
    return finalAnswer
    
    
# TEST STUFF
M1 = [[1, 2, 3], [-2, 3, 7]]
M2 = [[1,0,0],[0,1,0],[0,0,1]]
ans = array_mult(M1, M2)
print(ans)


M1 = [[1, 2, 3], [-2, 3, 7]]
M3 = [[1], [0], [-1]]
ans = array_mult(M1, M3)
print(ans)