code: function graph(g) {
      init(g);
  
      var xs = [upperLeft(g), upperRight(g), lowerRight(g), lowerLeft(g)];
  
      g.nodes().forEach(function(u) {
        var xArray = [];
        for (var i = 0; i < xs.length; ++i) {
          xArray.push(xs[i][u]);
        }
        xArray.sort();
        g.node(u).x = (xArray[1] + xArray[2]) / 2;
      });
    }
docs: /*
  Runs the position algorithm on the given graph with the configuration
  set in the instance of the position algorithm.