+void MTPGraph::compute_dp_ranks() {
+ Vertex *v;
+ Edge *e;
+
+ // This procedure computes for each node the longest link from the
+ // source and abort if the graph is not a DAG. It works by removing
+ // successively nodes without predecessor: At the first iteration it
+ // removes the source, then the nodes with incoming edge only from
+ // the source, etc. If it can remove all the nodes that way, the
+ // graph is a DAG. If at some point it can not remove node anymore
+ // and there are some remaining nodes, the graph is not a DAG. The
+ // rank of a node is the iteration at which is it removed, and we
+ // set the distance_from_source fields to this value.
+
+ Vertex **with_predecessor = new Vertex *[_nb_vertices];
+
+ // All the nodes are with_predecessor at first
+ for(int k = 0; k < _nb_vertices; k++) {
+ _vertices[k].distance_from_source = 0;
+ with_predecessor[k] = &_vertices[k];
+ }
+
+ scalar_t rank = 1;
+ int nb_with_predecessor = _nb_vertices, pred_nb_with_predecessor;
+
+ do {
+ // We set the distance_from_source field of all the vertices with incoming
+ // edges to the current rank value
+ for(int f = 0; f < nb_with_predecessor; f++) {
+ v = with_predecessor[f];
+ for(e = v->leaving_edge_list_root; e; e = e->next_leaving_edge) {
+ e->terminal_vertex->distance_from_source = rank;
+ }
+ }
+
+ pred_nb_with_predecessor = nb_with_predecessor;
+ nb_with_predecessor = 0;
+
+ // We keep all the vertices with incoming nodes
+ for(int f = 0; f < pred_nb_with_predecessor; f++) {
+ v = with_predecessor[f];
+ if(v->distance_from_source == rank) {
+ with_predecessor[nb_with_predecessor++] = v;
+ }
+ }
+
+ rank++;
+ } while(nb_with_predecessor < pred_nb_with_predecessor);
+
+ delete[] with_predecessor;
+
+ if(nb_with_predecessor > 0) {
+ cerr << __FILE__ << ": The graph is not a DAG." << endl;
+ abort();
+ }
+}
+
+//////////////////////////////////////////////////////////////////////
+