Numpy - Multiply each element of a matrix with the element of another matrix at the same position

Question

I'd like to multiply each element of a 3D matrix with the element of a same-sized matrix at the same position.

In 2D it'd look like:

Is there any clean solution with numpy other than for loops ?

EDIT: This matrix operation is named "Hadamard product"

Nicolas Gervais · Accepted Answer · 2020-03-09T16:22:30.937

2

Just multiply them. numpy supports matrix operations.

x = np.arange(1, 10).reshape(3, 3)

array([[1, 2, 3],
       [4, 5, 6],
       [7, 8, 9]])

print(x*x)

All elements will be multiplied by the respective number.

array([[ 1,  4,  9],
       [16, 25, 36],
       [49, 64, 81]])

edited Mar 09 '20 at 16:22

answered Mar 09 '20 at 16:17

Nicolas Gervais

Good answer, though the example provided doesn't necessarily demonstrate the element-wise nature of the result. – Thomas Kimber Mar 09 '20 at 16:20
you're right, i changed the example. – Nicolas Gervais Mar 09 '20 at 16:23
This would do matrix multiplication, not element wise multiplication like the OP is asking – Bengi Koseoglu Nov 04 '20 at 10:51

score 0 · Answer 2 · answered Mar 09 '20 at 16:17

0

You can use simple * to to element-wise multiplication with numpy arrays.

a = np.array([[1,2],[3,4]])
b = np.array([[1,2],[3,4]])

print(a*b)

Will give you

[[ 1  4]
 [ 9 16]]

answered Mar 09 '20 at 16:17

ywbaek

2 Answers2