title: Creating array of arrays in numpy with different dimensions
body: <p>I'm trying to create an array of numpy arrays, each one with a different dimension.
  So far, it seems to be fine. For example, if I run:</p>
  
  <pre><code>np.array([np.zeros((10,3)), np.zeros((11,8))])
  </code></pre>
  
  <p>the result is:</p>
  
  <pre><code>array([ array([[ 0.,  0.,  0.],
         [ 0.,  0.,  0.],
         [ 0.,  0.,  0.],
         [ 0.,  0.,  0.],
         [ 0.,  0.,  0.],
         [ 0.,  0.,  0.],
         [ 0.,  0.,  0.],
         [ 0.,  0.,  0.],
         [ 0.,  0.,  0.],
         [ 0.,  0.,  0.]]),
         array([[ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
         [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
         [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
         [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
         [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
         [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
         [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
         [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
         [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
         [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
         [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.]])], dtype=object)
  </code></pre>
  
  <p>The dimension of the two matrices are completely different and the array is generated without any problem. However, if the first dimension of the two matrices is the same, it doesn't work anymore:</p>
  
  <pre><code>np.array([np.zeros((10,3)), np.zeros((10,8))])
  Traceback (most recent call last):
  
    File "&lt;ipython-input-123-97301e1424ae&gt;", line 1, in &lt;module&gt;
      a=np.array([np.zeros((10,3)), np.zeros((10,8))])
  
  ValueError: could not broadcast input array from shape (10,3) into shape (10)
  </code></pre>
  
  <p>What is going on?</p>
  
  <p>Thank you!</p>