code: function normalizeRanks(g) {
    var min = _.min(_.map(g.nodes(), function(v) { return g.node(v).rank; }));
    _.forEach(g.nodes(), function(v) {
      var node = g.node(v);
      if (_.has(node, "rank")) {
        node.rank -= min;
      }
    });
  }
docs: /*
  Adjusts the ranks for all nodes in the graph such that all nodes v have
  rank(v) >= 0 and at least one node w has rank(w) = 0.