Added README.md

[mtp.git] / mtp_graph.cc

diff --git a/mtp_graph.cc b/mtp_graph.cc
index 983e3a0..2cbb338 100644 (file)
--- a/mtp_graph.cc
+++ b/mtp_graph.cc
@@ -241,7 +241,7 @@ void MTPGraph::force_positivized_lengths() {
     }
   }
 #ifdef VERBOSE
-  cerr << __FILE__ << ": residual_error " << residual_error << " max_error " << residual_error << endl;
+  cerr << __FILE__ << ": residual_error " << residual_error << " max_error " << max_error << endl;
 #endif
 }
 
@@ -275,6 +275,7 @@ void MTPGraph::dp_compute_distances() {
 // pred_edge_toward_source.
 
 void MTPGraph::find_shortest_path() {
+  int heap_size;
   Vertex *v, *tv, **last_slot;
   Edge *e;
   scalar_t d;
@@ -284,11 +285,11 @@ void MTPGraph::find_shortest_path() {
     _vertices[k].pred_edge_toward_source = 0;
   }
 
-  int heap_size = _nb_vertices;
+  heap_size = _nb_vertices;
   _source->distance_from_source = 0;
   _source->decrease_distance_in_heap(_heap);
 
-   while(heap_size > 0) {
+  while(heap_size > 1) {
     // Get the closest to the source
     v = _heap[0];
 
@@ -297,7 +298,7 @@ void MTPGraph::find_shortest_path() {
     heap_size--;
     last_slot = _heap + heap_size;
     swap(*_heap, *last_slot); swap((*_heap)->heap_slot, (*last_slot)->heap_slot);
-    _heap[0]->increase_distance_in_heap(_heap, last_slot);
+    (*_heap)->increase_distance_in_heap(_heap, last_slot);
 
     // Now update the neighbors of the node currently closest to the
     // source
@@ -378,7 +379,7 @@ void MTPGraph::find_best_paths(scalar_t *lengths) {
   }
 }
 
-int MTPGraph::retrieve_one_path(Edge *e, Path *path) {
+int MTPGraph::retrieve_one_path(Edge *e, Path *path, int *used_edges) {
   Edge *f, *next = 0;
   int l = 0, nb_occupied_next;
 
@@ -395,7 +396,9 @@ int MTPGraph::retrieve_one_path(Edge *e, Path *path) {
 
     nb_occupied_next = 0;
     for(f = e->terminal_vertex->leaving_edge_list_root; f; f = f->next_leaving_edge) {
-      if(f->occupied) { nb_occupied_next++; next = f; }
+      if(f->occupied && !used_edges[f - _edges]) {
+        nb_occupied_next++; next = f;
+      }
     }
 
 #ifdef DEBUG
@@ -403,13 +406,10 @@ int MTPGraph::retrieve_one_path(Edge *e, Path *path) {
       cerr << __FILE__ << ": retrieve_one_path: Non-sink end point." << endl;
       abort();
     }
-
-    else if(nb_occupied_next > 1) {
-      cerr << __FILE__ << ": retrieve_one_path: Non node-disjoint paths." << endl;
-      abort();
-    }
 #endif
 
+    if(path) { used_edges[next - _edges] = 1; }
+
     e = next;
   }
 
@@ -423,23 +423,15 @@ int MTPGraph::retrieve_one_path(Edge *e, Path *path) {
 
 //////////////////////////////////////////////////////////////////////
 
-static int compare_vertices_on_distance(const void *v1, const void *v2) {
-  scalar_t delta =
-    (*((Vertex **) v1))->distance_from_source -
-    (*((Vertex **) v2))->distance_from_source;
-  if(delta < 0) return -1;
-  else if(delta > 0) return 1;
-  else return 0;
-}
-
 void MTPGraph::compute_dp_ordering() {
   Vertex *v;
   Edge *e;
   int ntv;
 
-  // This method computes for each node the length of the longest link
-  // from the source, and orders the node in _dp_order according to
-  // it. It aborts if the graph is not a DAG.
+  // This method orders the nodes by putting first the ones with no
+  // predecessors, then going on adding nodes whose predecessors have
+  // all been already added. Computing the distances from the source
+  // by visiting nodes in that order is equivalent to DP.
 
   int *nb_predecessors = new int[_nb_vertices];
 
@@ -463,12 +455,15 @@ void MTPGraph::compute_dp_ordering() {
     }
   }
 
-  scalar_t rank = 1;
   while(already_processed < front) {
+    // Here, nodes before already_processed can be ignored, nodes
+    // before front were set to 0 predecessors during the previous
+    // iteration. During this new iteration, we have to visit the
+    // successors of these ones only, since they are the only ones
+    // which may end up with no predecessors.
     new_front = front;
     while(already_processed < front) {
       v = *(already_processed++);
-      v->distance_from_source = rank;
       for(e = v->leaving_edge_list_root; e; e = e->next_leaving_edge) {
         ntv = int(e->terminal_vertex - _vertices);
         nb_predecessors[ntv]--;
@@ -479,7 +474,6 @@ void MTPGraph::compute_dp_ordering() {
       }
     }
     front = new_front;
-    rank++;
   }
 
   if(already_processed < _dp_order + _nb_vertices) {
@@ -488,9 +482,6 @@ void MTPGraph::compute_dp_ordering() {
   }
 
   delete[] nb_predecessors;
-
-  for(int v = 0; v < _nb_vertices; v++) { _dp_order[v] = &_vertices[v]; }
-  qsort(_dp_order, _nb_vertices, sizeof(Vertex *), compare_vertices_on_distance);
 }
 
 //////////////////////////////////////////////////////////////////////
@@ -498,6 +489,7 @@ void MTPGraph::compute_dp_ordering() {
 void MTPGraph::retrieve_disjoint_paths() {
   Edge *e;
   int p, l;
+  int *used_edges;
 
   for(int p = 0; p < nb_paths; p++) delete paths[p];
   delete[] paths;
@@ -508,14 +500,21 @@ void MTPGraph::retrieve_disjoint_paths() {
   }
 
   paths = new Path *[nb_paths];
+  used_edges = new int[_nb_edges];
+  for(int e = 0; e < _nb_edges; e++) {
+    used_edges[e] = 0;
+  }
 
   p = 0;
   for(e = _source->leaving_edge_list_root; e; e = e->next_leaving_edge) {
-    if(e->occupied) {
-      l = retrieve_one_path(e, 0);
+    if(e->occupied && !used_edges[e - _edges]) {
+      l = retrieve_one_path(e, 0, used_edges);
       paths[p] = new Path(l);
-      retrieve_one_path(e, paths[p]);
+      retrieve_one_path(e, paths[p], used_edges);
+      used_edges[e - _edges] = 1;
       p++;
     }
   }
+
+  delete[] used_edges;
 }