/// graph can be indiced by two integer \c (i,j) value where \c i

   /// graph can be indiced by two integer \c (i,j) value where \c i

   /// is in the \c [0,height) range and j is in the [0, width) range.

   /// is in the \c [0,height) range and j is in the [0, width) range.

   /// Two nodes are connected in the graph if the indices differ only

   /// Two nodes are connected in the graph if the indices differ only

   /// on one position and only one is the difference. 

   /// on one position and only one is the difference. 

   ///

   ///

   /// \code

   /// \code

   /// MatrixGraph graph(h, w);

   /// MatrixGraph graph(h, w);

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

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

   /// for (int i = 0; i < graph.height(); ++i) {

   /// for (int i = 0; i < graph.height(); ++i) {

   ///   for (int j = 0; j < graph.width(); ++j) {

   ///   for (int j = 0; j < graph.width(); ++j) {