From: Francois Fleuret <francois@fleuret.org>
Date: Wed, 19 Dec 2012 13:23:13 +0000 (+0100)
Subject: Seems to work. Lot of debugging garbage still in there.
X-Git-Url: https://fleuret.org/cgi-bin/gitweb/gitweb.cgi?a=commitdiff_plain;h=2b3a2e10ec226f1610b9c39abd20f0899a34a652;p=mtp.git

Seems to work. Lot of debugging garbage still in there.
---

diff --git a/mtp_graph.cc b/mtp_graph.cc
index 5371732..12017c2 100644
--- a/mtp_graph.cc
+++ b/mtp_graph.cc
@@ -50,6 +50,8 @@ public:
   int last_change; // Used to mark which edges have already been
                    // processed in some methods
 
+  Vertex **heap_position;
+
   Vertex();
 
   inline void add_leaving_edge(Edge *e);
@@ -95,6 +97,10 @@ void Vertex::del_leaving_edge(Edge *e) {
 
 //////////////////////////////////////////////////////////////////////
 
+static int compare_vertex(const void *v1, const void *v2) {
+  return (*((Vertex **) v1))->last_change - (*((Vertex **) v2))->last_change;
+}
+
 MTPGraph::MTPGraph(int nb_vertices, int nb_edges,
                    int *vertex_from, int *vertex_to,
                    int source, int sink) {
@@ -103,8 +109,8 @@ MTPGraph::MTPGraph(int nb_vertices, int nb_edges,
 
   _edges = new Edge[_nb_edges];
   _vertices = new Vertex[_nb_vertices];
-  _front = new Vertex *[_nb_vertices];
-  _new_front = new Vertex *[_nb_vertices];
+  _heap = new Vertex *[_nb_vertices];
+  _dp_order = new Vertex *[_nb_vertices];
 
   _source = &_vertices[source];
   _sink = &_vertices[sink];
@@ -116,15 +122,31 @@ MTPGraph::MTPGraph(int nb_vertices, int nb_edges,
     _edges[e].terminal_vertex = _vertices + vertex_to[e];
   }
 
+  for(int v = 0; v < _nb_vertices; v++) {
+    _heap[v] = &_vertices[v];
+    _vertices[v].heap_position = &_heap[v];
+  }
+
   paths = 0;
   nb_paths = 0;
+
+  if(is_dag()) {
+    // Here the last_change field of every vertex tells us how many
+    // iterations of DP we need to reach it. Hence we only have to
+    // process the vertex in that order.
+    for(int v = 0; v < _nb_vertices; v++) { _dp_order[v] = &_vertices[v]; }
+    qsort(_dp_order, _nb_vertices, sizeof(Vertex *), compare_vertex);
+  } else {
+    cerr << __FILE__ << ": This graph is not a DAG." << endl;
+    abort();
+  }
 }
 
 MTPGraph::~MTPGraph() {
   delete[] _vertices;
+  delete[] _dp_order;
+  delete[] _heap;
   delete[] _edges;
-  delete[] _front;
-  delete[] _new_front;
   for(int p = 0; p < nb_paths; p++) delete paths[p];
   delete[] paths;
 }
@@ -213,40 +235,170 @@ int MTPGraph::is_dag() {
   Vertex *v;
   Edge *e;
 
-  // We put everybody in the front
+  Vertex **active = new Vertex *[_nb_vertices];
+
+  // We put everybody in the active
   for(int k = 0; k < _nb_vertices; k++) {
-    _vertices[k].last_change = -1;
-    _front[k] = &_vertices[k];
+    _vertices[k].last_change = 0;
+    active[k] = &_vertices[k];
   }
 
-  int iteration = 0;
-  int front_size = _nb_vertices, pred_front_size;
+  int iteration = 1;
+  int nb_active = _nb_vertices, pred_nb_active;
 
   do {
     // We set the last_change field of all the vertices with incoming
     // edges to the current iteration value
-    for(int f = 0; f < front_size; f++) {
-      v = _front[f];
+    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->last_change = iteration;
       }
     }
 
-    pred_front_size = front_size;
-    front_size = 0;
+    pred_nb_active = nb_active;
+    nb_active = 0;
 
     // We keep all the vertices with incoming nodes
-    for(int f = 0; f < pred_front_size; f++) {
-      v = _front[f];
+    for(int f = 0; f < pred_nb_active; f++) {
+      v = active[f];
       if(v->last_change == iteration) {
-        _front[front_size++] = v;
+        active[nb_active++] = v;
       }
     }
 
     iteration++;
-  } while(front_size < pred_front_size);
+  } while(nb_active < pred_nb_active);
+
+  delete[] active;
+
+  return nb_active == 0;
+}
+
+#ifdef DEBUG
+void print_heap(int first, int heap_size, Vertex **heap, int depth, Vertex *vertices) {
+  // if(depth == 0) cout << "** START_HEAP ********************************************************" << endl;
+  // if(first < heap_size) {
+    // print_heap((first + 1) * 2 - 1, heap_size, heap, depth + 1, vertices);
+    // for(int d = 0; d < depth; d++) cout << "  ";
+    // cout << "[" << heap[first] - vertices << "] ";
+    // if(heap[first]->distance_from_source == FLT_MAX) cout << "inf";
+    // else cout << heap[first]->distance_from_source;
+    // cout << endl;
+    // print_heap((first + 1) * 2, heap_size, heap, depth + 1, vertices);
+  // }
+  // if(depth == 0) cout << "** END_HEAP **********************************************************" << endl;
+}
+
+void check_heap(Vertex **heap, int heap_size, Vertex *vertices, int nb_vertices) {
+  Vertex **p, **h;
+  int *used = new int[nb_vertices];
+  for(int v = 0; v < nb_vertices; v++) used[v] = 0;
+  for(int k = 0; k < heap_size; k++) {
+    used[heap[k] - vertices]++;
+    h = heap + k;
+    if(h != (*h)->heap_position) abort();
+    if(k > 0) {
+      p = heap + (h - heap + 1) / 2 - 1;
+      if((*h)->distance_from_source < (*p)->distance_from_source) abort();
+    }
+  }
+  for(int v = 0; v < nb_vertices; v++) {
+    cout << used[v];
+    if(used[v] > 1) abort();
+  }
+  cout << endl;
+  delete[] used;
+}
+#endif
 
-  return front_size == 0;
+void MTPGraph::decrease_distance_in_heap(Vertex *v) {
+#ifdef DEBUG
+  // cout << "START decrease_distance_in_heap" << endl;
+  // print_heap(0, _heap_size, _heap, 0, _vertices);
+#endif
+  Vertex **p, **h;
+  // There is some beauty in that
+  h = v->heap_position;
+  while(h > _heap &&
+        (p = _heap + (h - _heap + 1) / 2 - 1,
+         (*p)->distance_from_source > (*h)->distance_from_source)) {
+// #warning REMOVE
+    // cout << "SWAP [" << (*p) - _vertices << " | " << (*h) - _vertices << "]" << endl;
+    // if((*p) - _vertices == 6 && (*h) - _vertices == 96) abort();
+    swap(*p, *h);
+    swap((*p)->heap_position, (*h)->heap_position);
+    h = p;
+  }
+#ifdef DEBUG
+  // check_heap(_heap, _heap_size, _vertices, _nb_vertices);
+  // print_heap(0, _heap_size, _heap, 0, _vertices);
+#endif
+}
+
+void MTPGraph::increase_distance_in_heap(Vertex *v) {
+#ifdef DEBUG
+  // cout << "START increase_distance_in_heap" << endl;
+  // print_heap(0, _heap_size, _heap, 0, _vertices);
+#endif
+  Vertex **c1, **c2, **h;
+  // There is some beauty in that
+  h = v->heap_position;
+  while(c1 = _heap + 2 * (h - _heap + 1) - 1, c2 = c1 + 1,
+        (c1 < _heap + _heap_size &&
+         (*c1)->distance_from_source < (*h)->distance_from_source)
+        ||
+        (c2 < _heap + _heap_size &&
+          (*c2)->distance_from_source < (*h)->distance_from_source)
+        ) {
+    if(c1 < _heap + _heap_size &&
+       !(c2 < _heap + _heap_size &&
+         (*c2)->distance_from_source < (*c1)->distance_from_source)){
+      swap(*c1, *h);
+      swap((*c1)->heap_position, (*h)->heap_position);
+      h = c1;
+    } else {
+      swap(*c2, *h);
+      swap((*c2)->heap_position, (*h)->heap_position);
+      h = c2;
+    }
+  }
+#ifdef DEBUG
+  // check_heap(_heap, _heap_size, _vertices, _nb_vertices);
+  // print_heap(0, _heap_size, _heap, 0, _vertices);
+#endif
+}
+
+void MTPGraph::dp_distance_propagation() {
+  Vertex *v, *tv;
+  Edge *e;
+  scalar_t d;
+
+  for(int k = 0; k < _nb_vertices; k++) {
+    _vertices[k].distance_from_source = FLT_MAX;
+    _vertices[k].pred_edge_toward_source = 0;
+  }
+
+  _source->distance_from_source = 0;
+
+  for(int k = 0; k < _nb_vertices; k++) {
+    v = _dp_order[k];
+    for(e = v->leaving_edges; e; e = e->next_leaving_edge) {
+      d = v->distance_from_source + e->positivized_length;
+      tv = e->terminal_vertex;
+      if(d < tv->distance_from_source) {
+        tv->distance_from_source = d;
+        tv->pred_edge_toward_source = e;
+        decrease_distance_in_heap(tv);
+      }
+    }
+  }
+
+#ifdef DEBUG
+  for(int k = 0; k < _nb_vertices; k++) {
+    if(_vertices[k].distance_from_source == FLT_MAX) abort();
+  }
+#endif
 }
 
 // This method does not change the edge occupation. It only set
@@ -254,7 +406,6 @@ int MTPGraph::is_dag() {
 // pred_edge_toward_source.
 
 void MTPGraph::find_shortest_path() {
-  Vertex **tmp_front;
   Vertex *v, *tv;
   Edge *e;
   scalar_t d;
@@ -264,7 +415,7 @@ void MTPGraph::find_shortest_path() {
     cout << "find_shortest_path: DAG -> ok" << endl;
   } else {
     for(int e = 0; e < _nb_edges; e++) {
-      if(_edges[e].positivized_length < 0)  abort();
+      if(_edges[e].positivized_length < 0) abort();
     }
     cout << "find_shortest_path: All positivized_length are positive -> ok" << endl;
   }
@@ -273,40 +424,54 @@ void MTPGraph::find_shortest_path() {
   for(int k = 0; k < _nb_vertices; k++) {
     _vertices[k].distance_from_source = FLT_MAX;
     _vertices[k].pred_edge_toward_source = 0;
-    _vertices[k].last_change = -1;
   }
 
-  int iteration = 0;
-
-  int front_size = 0, new_front_size;
-  _front[front_size++] = _source;
+  _heap_size = _nb_vertices;
   _source->distance_from_source = 0;
+  decrease_distance_in_heap(_source);
 
   do {
-    new_front_size = 0;
+#ifdef DEBUG
+    for(int k = 0; k < _heap_size; k++) {
+      if(_heap[0]->distance_from_source > _heap[k]->distance_from_source) abort();
+    }
+    // cout << "OK!" << endl;
+#endif
 
-    for(int f = 0; f < front_size; f++) {
-      v = _front[f];
-      for(e = v->leaving_edges; e; e = e->next_leaving_edge) {
-        d = v->distance_from_source + e->positivized_length;
-        tv = e->terminal_vertex;
-        if(d < tv->distance_from_source) {
-          tv->distance_from_source = d;
-          tv->pred_edge_toward_source = e;
-          if(tv->last_change < iteration) {
-            _new_front[new_front_size++] = tv;
-            tv->last_change = iteration;
-          }
-        }
+    v = _heap[0];
+    _heap_size--;
+    Vertex **a = _heap, **b = _heap + _heap_size;
+    swap(*a, *b); swap((*a)->heap_position, (*b)->heap_position);
+    increase_distance_in_heap(_heap[0]);
+
+    for(e = v->leaving_edges; e; e = e->next_leaving_edge) {
+      d = v->distance_from_source + e->positivized_length;
+      tv = e->terminal_vertex;
+      if(d < tv->distance_from_source) {
+        ASSERT(tv->heap_position - _heap < _heap_size);
+        tv->distance_from_source = d;
+        tv->pred_edge_toward_source = e;
+        decrease_distance_in_heap(tv);
+      }
+#ifdef DEBUG
+      for(int k = 0; k < _heap_size; k++) {
+        if(_heap[0]->distance_from_source > _heap[k]->distance_from_source) abort();
       }
+#endif
     }
+  } while(_heap_size > 0);
 
-    tmp_front = _new_front; _new_front = _front; _front = tmp_front;
-
-    front_size = new_front_size;
-
-    iteration++;
-  } while(front_size > 0);
+#ifdef DEBUG
+  for(int k = 0; k < _nb_vertices; k++) {
+    v = &_vertices[k];
+    for(e = v->leaving_edges; e; e = e->next_leaving_edge) {
+      d = v->distance_from_source + e->positivized_length;
+      tv = e->terminal_vertex;
+      if(d < tv->distance_from_source) abort();
+    }
+  }
+#endif
+  cout << "DONE!" << endl;
 }
 
 void MTPGraph::find_best_paths(scalar_t *lengths) {
@@ -320,10 +485,12 @@ void MTPGraph::find_best_paths(scalar_t *lengths) {
     _edges[e].positivized_length = _edges[e].length;
   }
 
-  // We call find_shortest_path here to set properly the distances to
-  // the source, so that we can make all the edge lengths positive at
-  // the first iteration.
-  find_shortest_path();
+  // // We call find_shortest_path here to set properly the distances to
+  // // the source, so that we can make all the edge lengths positive at
+  // // the first iteration.
+  // find_shortest_path();
+
+  dp_distance_propagation();
 
   do {
     update_positivized_lengths();
diff --git a/mtp_graph.h b/mtp_graph.h
index f28e460..5842671 100644
--- a/mtp_graph.h
+++ b/mtp_graph.h
@@ -49,6 +49,13 @@ class MTPGraph {
   // the total correction when compiled in VERBOSE mode.
   void force_positivized_lengths();
 
+  void decrease_distance_in_heap(Vertex *v);
+  void increase_distance_in_heap(Vertex *v);
+
+  // Visit the vertices according to _dp_order and simply update their
+  // distance to the source
+  void dp_distance_propagation();
+
   // Set in every vertex pred_edge_toward_source correspondingly to
   // the path of shortest length. The current implementation is not
   // Dijkstra's!
@@ -59,17 +66,24 @@ class MTPGraph {
   // nodes met along the path, and computes path->length properly.
   int retrieve_one_path(Edge *e, Path *path);
 
-  // Returns if the graph is a DAG
+  // Returns if the graph is a DAG, and set the last_change field of
+  // each vertex to the maximum number of iterations required to reach
+  // it
   int is_dag();
 
-  Vertex **_front, **_new_front;
-
   int _nb_vertices, _nb_edges;
   Vertex *_source, *_sink;
 
   Edge *_edges;
   Vertex *_vertices;
 
+  // For the shortest path search
+
+  Vertex **_heap;
+  int _heap_size;
+
+  Vertex **_dp_order;
+
 public:
 
   // These variables are filled when retrieve_disjoint_paths is called