title: How do I visualize a 3 dimensional matrix?
body: <p>How do I visualize a 3 dimensional matrix?</p>
  
  <p><img src="https://i.stack.imgur.com/kHRww.jpg" alt=""></p>
  
  <ul>
  <li>first dimension is x-coordinate  =  different universities  </li>
  <li>second dimension is y-coordinate  =  disciplines or specialties (Physics, Mathematics, Art ...)</li>
  <li>third dimension is color  =  different years</li>
  <li>size of the circles =  number of papers in corresponding  discipline/university</li>
  </ul>