anchor.diff:  
         node.select("circle")
             .style("fill", color);
  +
  +      // Update links.
  +      link = link.data(links, function(d) { return d.target.id; });
  +
  +      link.exit().remove();
  +
  +      link.enter().insert("line", ".node")
  +          .attr("class", "link");
  +
       }
   
       function tick() {
  
positive.code:       // Initialize the display to show a few nodes.
        // from: http://stackoverflow.com/questions/17504136/starting-d3-force-layout-collapsed-text-labels-duplicating
        function collapseAll(d) {
            if (d.children) {
              console.log('.');
              d.children.forEach(collapseAll);
              toggle(d);
            }
          }
          root.children.forEach(collapseAll);
          update(root);
  
      });
  
      function update() {
  
negative.code:         root;
  
      var force = d3.layout.force()
          .linkDistance(200)
          .charge(-670)
          .gravity(.05)
          .size([width, height])
          .on("tick", tick);
  