title: Graphviz top to bottom AND left to right
body: <p>Hi there I want to have a uml sequence diagram with dot language, now I have the following problem I want to have the layout as follows with a, b, c and d in a straight line at top but with the lines going straight to the bottom. How can I achieve that?</p>
  
  <pre><code>a   b   c   d
  |   |   |   | 
  |   |   |   |
  </code></pre>
  
  <p>perhaps can I achieve that the a, b, c and d with its belonging edges are clusters where I set a different rankdir for the clusters?</p>
  
  <p><strong>EDIT</strong> Just found a solution by adding invisible edges between a, b, c and d but any other solutions?</p>