multiplying a matrix by a 1d array-CodePudding

I need to multiply a matrix, e.g. a numpy array A with dimensions[3x2] by a 1d array B, of dimensions [1x4] to produce an array C of 4 [3x2] matrices, i.e. [4 x [3x2] ]

So for example C[0] would be a [3x2] matrix = A*B[0]

C[1] = A*B[1]

etc.

without a for i in B loop, but as a 1 line operation.

CodePudding user response：

Use broadcasting:

>>> a = np.arange(6).reshape(3, 2)
>>> a
array([[0, 1],
       [2, 3],
       [4, 5]])
>>> b = np.arange(4).reshape(1, 4)
>>> b
array([[0, 1, 2, 3]])
>>> c = b[None].T * a # Multiply (4, 1, 1) with (3, 2)
>>> c
array([[[ 0,  0],
        [ 0,  0],
        [ 0,  0]],

       [[ 0,  1],
        [ 2,  3],
        [ 4,  5]],

       [[ 0,  2],
        [ 4,  6],
        [ 8, 10]],

       [[ 0,  3],
        [ 6,  9],
        [12, 15]]])
>>> c.shape
(4, 3, 2)