[FIXED] Scaling a matrix by multiple elements of a numpy array

Issue

Assume we have a 4*4 matrix F in a numpy array with shape (4, 4)

F=np.array([[ 0,  1,  2,  3],
            [ 4,  5,  6,  7],
            [ 8,  9, 10, 11],
            [12, 13, 14, 15]])

and we want to scale F by every elements in matrix A of shape (3,2)

A=np.array([[0, 1],
            [2, 3],
            [4, 5]]) 

so the output is a np.array of shape (3, 2, 4, 4) (containing all the 6 scaled matrices of F) like this:

output=array([[[[ 0,  0,  0,  0],
                [ 0,  0,  0,  0],
                [ 0,  0,  0,  0],
                [ 0,  0,  0,  0]],

              [[ 0,  1,  2,  3],
               [ 4,  5,  6,  7],
               [ 8,  9, 10, 11],
               [12, 13, 14, 15]]],


             [[[ 0,  2,  4,  6],
               [ 8, 10, 12, 14],
               [16, 18, 20, 22],
               [24, 26, 28, 30]],

              [[ 0,  3,  6,  9],
               [12, 15, 18, 21],
               [24, 27, 30, 33],
               [36, 39, 42, 45]]],


             [[[ 0,  4,  8, 12],
               [16, 20, 24, 28],
               [32, 36, 40, 44],
               [48, 52, 56, 60]],

              [[ 0,  5, 10, 15],
               [20, 25, 30, 35],
               [40, 45, 50, 55],
               [60, 65, 70, 75]]]])

Solution

output = np.einsum('ij,kl->ijkl', A, F)

or

output = F * A.reshape((3,2,1,1))

Basically, all you need to do is reshape A in a way that each number is in its own nested list. i.e. [[[[[0]],[[1]]],[[[2]],[[3]]],[[[4]],[[5]]].

Answered By - dpkass