title: Tutorial for scipy.cluster.hierarchy
body: <p>I'm trying to understand how to manipulate a hierarchy cluster but the documentation is too ... technical?... and I can't understand how it works. </p>
  
  <p>Is there any tutorial that can help me to start with, explaining step by step some simple tasks?</p>
  
  <p>Let's say I have the following data set:</p>
  
  <pre><code>a = np.array([[0,   0  ],
                [1,   0  ],
                [0,   1  ],
                [1,   1  ], 
                [0.5, 0  ],
                [0,   0.5],
                [0.5, 0.5],
                [2,   2  ],
                [2,   3  ],
                [3,   2  ],
                [3,   3  ]])
  </code></pre>
  
  <p>I can easily do the hierarchy cluster and plot the dendrogram:</p>
  
  <pre><code>z = linkage(a)
  d = dendrogram(z)
  </code></pre>
  
  <ul>
  <li>Now, how I can recover a specific cluster? Let's say the one with elements <code>[0,1,2,4,5,6]</code> in the dendrogram?</li>
  <li>How I can get back the values of that elements?   </li>
  </ul>