title: Multiply 2D NumPy arrays element-wise and sum
body: <p>I am wondering if there is a quicker way/dedicated NumPy function to perform element-wise multiplication of 2D NumPy arrays and then sum all the elements.
  I currently use <code>np.sum(np.multiply(A, B))</code> where A, B are NumPy arrays of equal dimension <code>m x n</code>.</p>