The result of `Y @ X` has shape (3,), so the next line (concatenate as columns) fails.

To make `Z` a column vector, we would need something like `Z = (Y @ X)[:,np.newaxis]`.

Although, I'm not sure why the author is using `concatenate` when the more idiomatic function would be stack, so the change you suggest works and is pretty clean:

   Z = Y @ X
   np.stack([Z, Z], axis=1)
   # array([[14, 14],
   #        [32, 32],
   #        [50, 50]])

with convention that vectors are shape (3,) instead of (3,1).