X-Git-Url: https://www.fleuret.org/cgi-bin/gitweb/gitweb.cgi?a=blobdiff_plain;f=mtp_graph.cc;h=682dd808e830eb4f36d99a02695d240fc3da3f50;hb=78b0bdef0b9a3479502c7598fd69a012c297e125;hp=2832e71f6ca8fcae738357e4c5872d4a39e9f442;hpb=276df8ea8b9761cc729048d8e5c42670debc5825;p=mtp.git

diff --git a/mtp_graph.cc b/mtp_graph.cc
index 2832e71..682dd80 100644
--- a/mtp_graph.cc
+++ b/mtp_graph.cc
@@ -53,7 +53,7 @@ public:
   inline void add_leaving_edge(Edge *e);
   inline void del_leaving_edge(Edge *e);
   inline void decrease_distance_in_heap(Vertex **heap);
-  inline void increase_distance_in_heap(Vertex **heap, int heap_size);
+  inline void increase_distance_in_heap(Vertex **heap, Vertex **heap_bottom);
 };
 
 //////////////////////////////////////////////////////////////////////
@@ -104,18 +104,18 @@ void Vertex::decrease_distance_in_heap(Vertex **heap) {
   }
 }
 
-void Vertex::increase_distance_in_heap(Vertex **heap, int heap_size) {
+void Vertex::increase_distance_in_heap(Vertex **heap, Vertex **heap_bottom) {
   Vertex **c1, **c2, **h;
   // omg, that's beautiful
   h = heap_slot;
   while(c1 = heap + 2 * (h - heap) + 1,
-        c1 < heap + heap_size &&
+        c1 < heap_bottom &&
         (c2 = c1 + 1,
          (*c1)->distance_from_source < (*h)->distance_from_source
          ||
-         (c2 < heap + heap_size && (*c2)->distance_from_source < (*h)->distance_from_source)
+         (c2 < heap_bottom && (*c2)->distance_from_source < (*h)->distance_from_source)
          )) {
-    if(c2 < heap + heap_size && (*c2)->distance_from_source <= (*c1)->distance_from_source) {
+    if(c2 < heap_bottom && (*c2)->distance_from_source <= (*c1)->distance_from_source) {
       swap(*c2, *h);
       swap((*c2)->heap_slot, (*h)->heap_slot);
       h = c2;
@@ -188,6 +188,60 @@ MTPGraph::~MTPGraph() {
   delete[] paths;
 }
 
+int 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_edges; 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;
+
+  return nb_with_predecessor == 0;
+}
+
 //////////////////////////////////////////////////////////////////////
 
 void MTPGraph::print(ostream *os) {
@@ -246,7 +300,6 @@ void MTPGraph::force_positivized_lengths() {
     Edge *e = _edges + k;
 
     if(e->positivized_length < 0) {
-
 #ifdef VERBOSE
       residual_error -= e->positivized_length;
       max_error = max(max_error, - e->positivized_length);
@@ -259,60 +312,6 @@ void MTPGraph::force_positivized_lengths() {
 #endif
 }
 
-int 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 **active = new Vertex *[_nb_vertices];
-
-  // All the nodes are active at first
-  for(int k = 0; k < _nb_vertices; k++) {
-    _vertices[k].distance_from_source = 0;
-    active[k] = &_vertices[k];
-  }
-
-  scalar_t rank = 1;
-  int nb_active = _nb_vertices, pred_nb_active;
-
-  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_active; f++) {
-      v = active[f];
-      for(e = v->leaving_edges; e; e = e->next_leaving_edge) {
-        e->terminal_vertex->distance_from_source = rank;
-      }
-    }
-
-    pred_nb_active = nb_active;
-    nb_active = 0;
-
-    // We keep all the vertices with incoming nodes
-    for(int f = 0; f < pred_nb_active; f++) {
-      v = active[f];
-      if(v->distance_from_source == rank) {
-        active[nb_active++] = v;
-      }
-    }
-
-    rank++;
-  } while(nb_active < pred_nb_active);
-
-  delete[] active;
-
-  return nb_active == 0;
-}
-
 void MTPGraph::dp_compute_distances() {
   Vertex *v, *tv;
   Edge *e;
@@ -333,7 +332,6 @@ void MTPGraph::dp_compute_distances() {
       if(d < tv->distance_from_source) {
         tv->distance_from_source = d;
         tv->pred_edge_toward_source = e;
-        tv->decrease_distance_in_heap(_heap);
       }
     }
   }
@@ -344,7 +342,7 @@ void MTPGraph::dp_compute_distances() {
 // pred_edge_toward_source.
 
 void MTPGraph::find_shortest_path() {
-  Vertex *v, *tv, **a, **b;
+  Vertex *v, *tv, **last_slot;
   Edge *e;
   scalar_t d;
 
@@ -361,15 +359,15 @@ void MTPGraph::find_shortest_path() {
     // Get the closest to the source
     v = _heap[0];
 
-    // Remove it from the heap (swap it with the last in the heap, and
+    // Remove it from the heap (swap it with the last_slot in the heap, and
     // update the distance of that one)
     _heap_size--;
-    a = _heap;
-    b = _heap + _heap_size;
-    swap(*a, *b); swap((*a)->heap_slot, (*b)->heap_slot);
-    _heap[0]->increase_distance_in_heap(_heap, _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, _heap + _heap_size);
 
-    // Now update the neighbors of the currently closest to the source
+    // Now update the neighbors of the node currently closest to the
+    // source
     for(e = v->leaving_edges; e; e = e->next_leaving_edge) {
       d = v->distance_from_source + e->positivized_length;
       tv = e->terminal_vertex;
@@ -384,7 +382,7 @@ void MTPGraph::find_shortest_path() {
 }
 
 void MTPGraph::find_best_paths(scalar_t *lengths) {
-  scalar_t total_length;
+  scalar_t shortest_path_length;
   Vertex *v;
   Edge *e;
 
@@ -394,15 +392,21 @@ void MTPGraph::find_best_paths(scalar_t *lengths) {
     _edges[e].positivized_length = _edges[e].length;
   }
 
-  // Update the distances to the source in "good order"
+  // Compute the distance of all the nodes from the source by just
+  // visiting them in the proper DAG ordering we computed when
+  // building the graph
   dp_compute_distances();
 
   do {
+    // Use the current distance from the source to make all edge
+    // lengths positive
     update_positivized_lengths();
+    // Fix numerical errors
     force_positivized_lengths();
+
     find_shortest_path();
 
-    total_length = 0.0;
+    shortest_path_length = 0.0;
 
     // Do we reach the sink?
     if(_sink->pred_edge_toward_source) {
@@ -410,13 +414,13 @@ void MTPGraph::find_best_paths(scalar_t *lengths) {
       // original edge lengths
       v = _sink;
       while(v->pred_edge_toward_source) {
-        total_length += v->pred_edge_toward_source->length;
+        shortest_path_length += v->pred_edge_toward_source->length;
         v = v->pred_edge_toward_source->origin_vertex;
       }
       // If that length is negative
-      if(total_length < 0.0) {
+      if(shortest_path_length < 0.0) {
 #ifdef VERBOSE
-        cerr << __FILE__ << ": Found a path of length " << total_length << endl;
+        cerr << __FILE__ << ": Found a path of length " << shortest_path_length << endl;
 #endif
         // Invert all the edges along the best path
         v = _sink;
@@ -431,7 +435,7 @@ void MTPGraph::find_best_paths(scalar_t *lengths) {
       }
     }
 
-  } while(total_length < 0.0);
+  } while(shortest_path_length < 0.0);
 
   // Put back the graph in its original state (i.e. invert edges which
   // have been inverted in the process)