/// arcs can be retrieved with the \c right(), \c up(), \c left()

   /// arcs can be retrieved with the \c right(), \c up(), \c left()

   /// and \c down() functions, where the bottom-left corner is the

   /// and \c down() functions, where the bottom-left corner is the

   /// origin.

   /// origin.

   ///

   ///

   /// \image html grid_graph.png

   /// \image html grid_graph.png

   ///

   ///

   /// A short example about the basic usage:

   /// A short example about the basic usage:

   ///\code

   ///\code

   /// GridGraph graph(rows, cols);

   /// GridGraph graph(rows, cols);

   /// GridGraph::NodeMap<int> val(graph);

   /// GridGraph::NodeMap<int> val(graph);