Python 3: Multiply a vector by a matrix without NumPy

Question

I'm fairly new to Python and trying to create a function to multiply a vector by a matrix (of any column size). e.g.:

multiply([1,0,0,1,0,0], [[0,1],[1,1],[1,0],[1,0],[1,1],[0,1]])

[1, 1]

Here is my code:

def multiply(v, G):
    result = []
    total = 0
    for i in range(len(G)):
        r = G[i]
        for j in range(len(v)):
            total += r[j] * v[j]
        result.append(total)
    return result  

The problem is that when I try to select the first row of each column in the matrix (r[j]) the error 'list index out of range' is shown. Is there any other way of completing the multiplication without using NumPy?

Answer 1

# check matrices
A = [[1,2],[3,4]]
B = [[1,4],[5,6],[7,8],[9,6]]

def custom_mm(A,B):    
    if len(A[0]) == len(B): -- condition to check if matrix multiplication is valid or not. Making sure matrix is nXm and mXy
        result = [] -- final matrix
        for i in range(0,len(A)): -- loop through each row of first matrix
            temp = [] -- temporary list to hold output of each row of the output matrix where number of elements will be column of second matrix
            for j in range(0,len(B[0])): -- loop through each column of second matrix
                total = 0 
                l = 0 -- dummy index to switch row of second matrix 
                for k in range(0,len(A[0])):
                    total += A[i][k]*B[l][j]
                    l = l+1
                temp.append(total)
            result.append(temp)                
        return result
    else:
        return (print("not possible"))

print(custom_mm(A,B))


    

Answer 2

i have attached a code for matrix multiplication do follow the example format for one dimensional multiplication (lists of list)

def MM(a,b):
c = []
for i in range(0,len(a)):
    temp=[]
    for j in range(0,len(b[0])):
        s = 0
        for k in range(0,len(a[0])):
            s += a[i][k]*b[k][j]
        temp.append(s)
    c.append(temp)

return c
a=[[1,2]]
b=[[1],[2]]
print(MM(a,b))

result is [[5]]