relaxVertex (digraph, vertex, tree) {
    const distTo = tree.distTo
    const edgeTo = tree.edgeTo

    digraph.getAdj(vertex).forEach(function (edge) {
      const w = edge.to()
      distTo[w] = distTo[w] || 0.0
      distTo[vertex] = distTo[vertex] || 0.0
      if (distTo[w] < distTo[vertex] + edge.weight) {
        // in case of the result of 0.28+0.34 is 0.62000001
        distTo[w] = parseFloat((distTo[vertex] + edge.weight).toFixed(2))
        edgeTo[w] = edge
      }
    })
  }
relax a vertex v in the specified digraph g
@param {EdgeWeightedDigraph} the apecified digraph
@param {Vertex} v vertex to be relaxed