Multiply each row of one array with each element of another array in numpy

Question

I have two arrays A and B in numpy. A holds cartesian coordinates, each row is one point in 3D space and has the shape (r, 3). B has the sh

Answer 1

Use broadcasting -

A[:,None,:]*B[:,:,None]

Since np.einsum also supports broadcasting, you can use that as well (thanks to @ajcr for suggesting this concise version) -

np.einsum('ij,ik->ikj',A,B)

Sample run -

In [22]: A
Out[22]: 
array([[1, 1, 1],
       [2, 2, 2],
       [3, 3, 3]])

In [23]: B
Out[23]: 
array([[10, 20],
       [30, 40],
       [50, 60]])

In [24]: A[:,None,:]*B[:,:,None]
Out[24]: 
array([[[ 10,  10,  10],
        [ 20,  20,  20]],

       [[ 60,  60,  60],
        [ 80,  80,  80]],

       [[150, 150, 150],
        [180, 180, 180]]])

In [25]: np.einsum('ijk,ij->ijk',A[:,None,:],B)
Out[25]: 
array([[[ 10,  10,  10],
        [ 20,  20,  20]],

       [[ 60,  60,  60],
        [ 80,  80,  80]],

       [[150, 150, 150],
        [180, 180, 180]]])