/*
Set the cut values of edges in the spanning tree by a depth-first
postorder traversal.  The cut value corresponds to the cost, in
terms of a ranking's edge length sum, of lengthening an edge.
Negative cut values typically indicate edges that would yield a
smaller edge length sum if they were lengthened.
function initCutValues(graph, spanningTree) {
  computeLowLim(spanningTree);

  spanningTree.eachEdge(function(id, u, v, treeValue) {
    treeValue.cutValue = 0;
  });

  // Propagate cut values up the tree.
  function dfs(n) {
    var children = spanningTree.successors(n);
    for (var c in children) {
      var child = children[c];
      dfs(child);
    }
    if (n !== spanningTree.graph().root) {
      setCutValue(graph, spanningTree, n);
    }
  }
  dfs(spanningTree.graph().root);
}