old_contents: (function(World, View){
      var world = new World();
  
      var problem = world.createInvertedPendulum();
  
      new View(document.getElementById('playground'), problem);
  })(World, InvertedPendulumView);
  
new_contents: (function(World, View){
      var world = new World();
  
      var problem = world.createInvertedPendulum({ angle: Math.PI/50 });
  
      new View(document.getElementById('playground'), problem);
  })(World, InvertedPendulumView);
  
subject: set initial angle off center