text: var tracer = new DirectedGraphTracer();
  var logger = new LogTracer();
  tracer.attach(logger);
  /*var G = [ // G[i][j] indicates whether the path from the i-th node to the j-th node exists or not
   [0, 1, 1, 1, 0],
   [0, 0, 1, 1, 1],
   [0, 0, 0, 0, 0],
   [0, 0, 0, 0, 1],
   [0, 0, 0, 0, 0]
   ];*/
  var G = DirectedGraph.random(5, .75);
  tracer._setData(G);