public Edge(Vertex u, Vertex v) {
			_u = u;
			_v = v;
		}
		public Edge(Vertex u, Vertex v, double weight) {
			_u = u;
			_v = v;
			_weight = weight;
		}
		public double weight(Vertex u, Vertex v) {
			return _matrix[u.Index, v.Index].Weight;
		}