title: Converting a list of 3d matrix into 4d matrix
body: <p>I am trying to write a function, which takes in a list of 3d matrices.. </p>
  
  <p>so.. each element in list have shape <code>(rows,cols, some_scalar).</code>.
  I am trying to reshape it into 4d matrix.. 
  so <code>output = (number_of_elements_in_matrix, rows,cols,some_scalar)</code></p>
  
  <p>so far I have is</p>
  
  <pre><code>output = np.zeros((len(list_of_matrices), list_of_matrices[0].shape[0], list_of_matrices[0].shape[1],
                        list_of_matrices[0].shape[2]), dtype=np.uint8)
  </code></pre>
  
  <p>How do i know fill this output 4d tensor with the values..</p>
  
  <pre><code>def reshape_matrix(list_of_matrices):
     output = np.zeros((len(list_of_matrices), list_of_matrices[0].shape[0], list_of_matrices[0].shape[1],
                            list_of_matrices[0].shape[2]), dtype=np.uint8)
  
  
     return output
  </code></pre>