title: Understanding np.ix_
body: <p>Code:</p>
  <pre><code>import numpy as np
  
  ray = [1,22,33,42,51], [61,71,812,92,103], [113,121,132,143,151], [16,172,183,19,201]
  ray = np.asarray(ray)
  type(ray)
  
  ray[np.ix_([-2:],[3:4])]
  
  </code></pre>
  <p>I'd like to use index slicing and get a subarray consisting of the last two rows and the 3rd/4th columns.  My current code produces an error:</p>
  <p>I'd also like to sum each column.  What am I doing wrong?  I cannot post a picture because I need at least 10 reputation points.</p>