\todo This subsection is under construction.

 If you would like to design an electric network minimizing the total length

 of wires, then you might be looking for a minimum spanning tree in an

 undirected graph.

 This can be found using the \ref kruskal() "Kruskal" algorithm.

 See \ref spantree for the minimum spanning tree algorithms and

 Let us suppose that the network is stored in a \ref ListGraph object \c g

 \ref matching for matching algorithms.

 with a cost map \c cost. We create a \c bool valued edge map \c tree_map or

 a vector \c tree_vector for stroing the tree that is found by the algorithm.

 After that, we could call the \ref kruskal() function. It gives back the weight

 of the minimum spanning tree and \c tree_map or \c tree_vector

 will contain the found spanning tree.

 If you want to store the arcs in a \c bool valued edge map, then you can use

 the function as follows.

 \code

   // Kruskal algorithm with edge map

   ListGraph::EdgeMap<bool> tree_map(g);

   std::cout << "The weight of the minimum spanning tree is "

             << kruskal(g, cost_map, tree_map) << std::endl;

   // Print the results

   std::cout << "Edges of the tree: " << std::endl;

   for (ListGraph::EdgeIt e(g); e != INVALID; ++e) {

     if (!tree_map[e]) continue;

     std::cout << "(" << g.id(g.u(e)) << ", " << g.id(g.v(e)) << ")\n";

   }

 \endcode

 If you would like to store the edges in a standard container, you can

 do it like this.

 \code

   // Kruskal algorithm with edge vector

   std::vector<ListGraph::Edge> tree_vector;

   std::cout << "The weight of the minimum spanning tree is "

             << kruskal(g, cost_map, tree_vector) << std::endl;

   // Print the results

   std::cout << "Edges of the tree: " << std::endl;

   for (unsigned i = 0; i != tree_vector.size(); ++i) {

     Edge e = tree_vector[i];

     std::cout << "(" << g.id(g.u(e)) << ", " << g.id(g.v(e)) << ")\n";

   }

 \endcode

 \todo \ref matching "matching algorithms".