I have two matrices to multiply. One is weight matrix - W whose size is 900x2x2.
Another is input matrix-I whose size is 2x2.
Now I want to perform summation over c = WI which will be 900x1 matrix,
but when I perform the operation it multiplies and gives me 900x2x2 matrix again.
Q 2) (related) So I made both of them 2D and multiplied 900x4 * 4x1 but that gives me an error saying
ValueError:operands could not be broadcast together with shapes (900,4) (4,1)
It seems you are trying to lose the last two axes of the first array against the only two axes of the second weight array with that matrix-multiplication. We could translate that idea into NumPy code with np.tensordot and assuming arr1 and arr2 as the input arrays respectively, like so -
np.tensordot(arr1,arr2,axes=([1,2],[0,1]))
Another simpler way to put into NumPy code would be with np.einsum, like so -
np.einsum('ijk,jk',arr1,arr2)
来源：https://stackoverflow.com/questions/38785566/multiplying-3d-matrix-with-2d-matrix