title: Too many indices in numpy array when calculating size
body: <pre><code>def reg_interval_size(self, prediction, y, significance):
      idx = int(significance * 100 - 1)
      prediction = prediction[:, idx]
      
      prediction_size = prediction[:, 1] - prediction[:, 0]
      
      return prediction_size
  </code></pre>
  <p>This is the error I am getting when applying the function:</p>
  <pre><code>IndexError: index 4 is out of bounds for axis 1 with size 2
  </code></pre>
  <p><strong>My prediction interval</strong></p>
  <pre><code>[[-0.08654671  0.7144939 ]
   [-0.61418434  0.18685626]
   [ 0.16648421  0.96752482]
   ...
   [ 0.01177342  0.81281403]
   [ 0.44408509  1.2451257 ]
   [ 0.37012494  1.17116555]]
  </code></pre>
  <h1>Example</h1>
  <pre><code>prediction_size = reg_interval_size(self, prediction, y, significance= 0.05):
  </code></pre>
  <p><strong>Expected Output</strong>
  (It is just a 1D array that calculates the difference in size between each row of the prediction interval array)</p>
  <pre><code>[0.80104061 0.80104061 0.80104061 ... 0.80104061 0.80104061 0.80104061]
  </code></pre>