title: Absolute difference of two NumPy arrays
body: <p>Is there an efficient way/function to subtract one matrix from another and writing the absolute values in a new matrix?
  I can do it entry by entry but for big matrices, this will be fairly slow...</p>
  
  <p>For example:</p>
  
  <pre><code>X = [[12,7,3],
  [4 ,5,6],
  [7 ,8,9]]
  
  Y = [[5,8,1],
  [6,7,3],
  [4,5,9]]
  
  for i in range(len(r_0)):
      for j in range(len(r)):
          delta_r[i][j]= sqrt((r[i][j])**2 - (r_0[i][j])**2)
  </code></pre>