title: How to create a nested matrix in python
body: <p>I was wondering if it was possible to create a nested matrix in python. Here I define my matrix <code>A</code></p>
  
  <pre><code>  A = array([[ 12.,   0.],[  0.,   4.]])
  </code></pre>
  
  <p>I would like to replace the zeros with a generic 2x2 matrix and then plot everything with <code>imshow()</code>. Is that possible?</p>
  
  <p>I tried defining my nested matrix this way </p>
  
  <pre><code>  A = array([[ 12.,   array([[ 1.,   1.],[  1.,   1.]])],[  0.,   4.]])
  </code></pre>
  
  <p>but I got this error message</p>
  
  <p>ValueError: setting an array element with a sequence.</p>