Why can't a 3, 2 matrix be multiplied by a 2, 2 matrix with NumPy?

Question

Using NumPy and attempting to multiply matrices together sometimes doesn't work. For example

import numpy as np

x = np.matrix('1, 2; 3, 8; 2, 9')
y = np.matrix('5, 4; 8, 2')

print(np.multiply(x, y))

can return

Traceback (most recent call last):
  File "vector-practice.py", line 6, in <module>
    print(np.multiply(x, y))
ValueError: operands could not be broadcast together with shapes (3,2) (2,2)

I understand that I can't multiply these shapes, but why not? I can multiply these two matrices on paper, so why not in NumPy? Am I missing something obvious here?

Answer 1

np.multiply Multiply arguments element-wise., it's not a matrix multiplication. When you have matrices, you need to use * or np.dot for matrix multiplication.

x * y
#matrix([[21,  8],
#        [79, 28],
#        [82, 26]])

np.dot(x, y)
#matrix([[21,  8],
#        [79, 28],
#        [82, 26]])