X-Git-Url: https://fleuret.org/cgi-bin/gitweb/gitweb.cgi?a=blobdiff_plain;f=mtp_graph.cc;h=ee6da31de61df9abe9705b41a895763b612ccd00;hb=8df7c7e77366cb95e9e8e963af9319d9cbac1934;hp=c2a7fa3e2a150ab06b575ddb84695cddf46f3984;hpb=ea33e3e5dddbe3796d2361910e1e3ed98a19865c;p=mtp.git

diff --git a/mtp_graph.cc b/mtp_graph.cc
index c2a7fa3..ee6da31 100644
--- a/mtp_graph.cc
+++ b/mtp_graph.cc
@@ -27,8 +27,12 @@ class Edge {
 public:
   int id, occupied;
   scalar_t length, work_length;
-  Vertex *terminal_vertex;
+  Vertex *origin_vertex, *terminal_vertex;
+
+  // These are the links in the origin_vertex leaving edge list
   Edge *next, *pred;
+
+  inline void revert();
 };
 
 class Vertex {
@@ -36,131 +40,139 @@ public:
   int id, iteration;
   Edge *root_edge;
   scalar_t distance_from_source;
-  Vertex *pred_vertex;
-  Edge *pred_edge;
+  Edge *best_pred_edge_to_source;
 
-  Vertex() { root_edge = 0; }
+  Vertex();
+  inline void add_edge(Edge *e);
+  inline void del_edge(Edge *e);
+};
 
-  inline void add_edge(Edge *e) {
-    e->next = root_edge;
-    e->pred = 0;
-    if(root_edge) { root_edge->pred = e; }
-    root_edge = e;
-  }
+//////////////////////////////////////////////////////////////////////
 
-  inline void del_edge(Edge *e) {
-    if(e == root_edge) { root_edge = e->next; }
-    if(e->pred) { e->pred->next = e->next; }
-    if(e->next) { e->next->pred = e->pred; }
-  }
-};
+void Edge::revert() {
+  length = - length;
+  work_length = 0;
+  origin_vertex->del_edge(this);
+  terminal_vertex->add_edge(this);
+  Vertex *t = terminal_vertex;
+  terminal_vertex = origin_vertex;
+  origin_vertex = t;
+}
+
+//////////////////////////////////////////////////////////////////////
+
+Vertex::Vertex() {
+  root_edge = 0;
+}
+
+void Vertex::add_edge(Edge *e) {
+  e->next = root_edge;
+  e->pred = 0;
+  if(root_edge) { root_edge->pred = e; }
+  root_edge = e;
+}
+
+void Vertex::del_edge(Edge *e) {
+  if(e == root_edge) { root_edge = e->next; }
+  if(e->pred) { e->pred->next = e->next; }
+  if(e->next) { e->next->pred = e->pred; }
+}
+
+//////////////////////////////////////////////////////////////////////
 
 void MTPGraph::print() {
-  for(int n = 0; n < _nb_vertices; n++) {
-    for(Edge *e = vertices[n].root_edge; e; e = e->next) {
-      cout << n << " -> " << e->terminal_vertex->id << " " << e->length;
-      if(e->occupied) {
-        cout << " *";
-      }
-      cout << endl;
+  for(int k = 0; k < _nb_edges; k++) {
+    Edge *e = _edges + k;
+    cout << e->origin_vertex->id
+         << " -> "
+         << e->terminal_vertex->id
+         << " "
+         << e->length;
+    if(e->occupied) {
+      cout << " *";
     }
+    cout << endl;
   }
 }
 
 void MTPGraph::print_dot() {
   cout << "digraph {" << endl;
   cout << "  node[shape=circle];" << endl;
-  for(int n = 0; n < _nb_vertices; n++) {
-    int a = vertices[n].id;
-    for(Edge *e = vertices[n].root_edge; e; e = e->next) {
-      int b = e->terminal_vertex->id;
-      if(e->occupied) {
-        cout << "  " << b << " -> " << a << " [style=bold,color=black,label=\"" << -e->length << "\"];" << endl;
-      } else {
-        cout << "  " << a << " -> " << b << " [color=gray,label=\"" << e->length << "\"];" << endl;
-      }
+  for(int k = 0; k < _nb_edges; k++) {
+    Edge *e = _edges + k;
+    if(e->occupied) {
+      cout << "  " << e->origin_vertex->id << " -> " << e->terminal_vertex->id
+           << " [style=bold,color=black,label=\"" << -e->length << "\"];" << endl;
+    } else {
+      cout << "  " << e->origin_vertex->id << " -> " << e->terminal_vertex->id
+           << " [color=gray,label=\"" << e->length << "\"];" << endl;
     }
   }
   cout << "}" << endl;
 }
 
-
-void dot_print(int nb_vertices,
-               int nb_edges, int *ea, int *eb, scalar_t *el,
-               int _source, int _sink,
-               int *edge_occupation) {
-  for(int e = 0; e < nb_edges; e++) {
-  }
-  cout << "}" << endl;
-}
 MTPGraph::MTPGraph(int nb_vertices, int nb_edges,
                    int *from, int *to,
-                   int src, int snk) {
+                   int source, int sink) {
   _nb_vertices = nb_vertices;
   _nb_edges = nb_edges;
 
-  edges = new Edge[_nb_edges];
-  vertices = new Vertex[_nb_vertices];
+  _edges = new Edge[_nb_edges];
+  _vertices = new Vertex[_nb_vertices];
+  _front = new Vertex *[_nb_vertices];
+  _new_front = new Vertex *[_nb_vertices];
 
-  _source = &vertices[src];
-  _sink = &vertices[snk];
+  _source = &_vertices[source];
+  _sink = &_vertices[sink];
 
   for(int v = 0; v < _nb_vertices; v++) {
-    vertices[v].id = v;
+    _vertices[v].id = v;
   }
 
   for(int e = 0; e < nb_edges; e++) {
-    vertices[from[e]].add_edge(&edges[e]);
-    edges[e].occupied = 0;
-    edges[e].id = e;
-    edges[e].terminal_vertex = &vertices[to[e]];
+    _vertices[from[e]].add_edge(_edges + e);
+    _edges[e].occupied = 0;
+    _edges[e].id = e;
+    _edges[e].origin_vertex = _vertices + from[e];
+    _edges[e].terminal_vertex = _vertices + to[e];
   }
 
-  _front = new Vertex *[_nb_vertices];
-  _new_front = new Vertex *[_nb_vertices];
 }
 
 MTPGraph::~MTPGraph() {
-  delete[] vertices;
-  delete[] edges;
+  delete[] _vertices;
+  delete[] _edges;
   delete[] _front;
   delete[] _new_front;
 }
 
-void MTPGraph::initialize_work_lengths() {
+void MTPGraph::initialize_work_lengths_with_min() {
   scalar_t length_min = 0;
   for(int n = 0; n < _nb_vertices; n++) {
-    for(Edge *e = vertices[n].root_edge; e; e = e->next) {
+    for(Edge *e = _vertices[n].root_edge; e; e = e->next) {
       length_min = min(e->length, length_min);
     }
   }
   for(int n = 0; n < _nb_vertices; n++) {
-    for(Edge *e = vertices[n].root_edge; e; e = e->next) {
+    for(Edge *e = _vertices[n].root_edge; e; e = e->next) {
       e->work_length = e->length - length_min;
     }
   }
 }
 
-void MTPGraph::update_work_length() {
-  for(int n = 0; n < _nb_vertices; n++) {
-    scalar_t d = vertices[n].distance_from_source;
-    for(Edge *e = vertices[n].root_edge; e; e = e->next) {
-      e->work_length += d - e->terminal_vertex->distance_from_source;
-    }
+void MTPGraph::update_work_lengths() {
+  for(int k = 0; k < _nb_edges; k++) {
+    Edge *e = _edges + k;
+    e->work_length += e->terminal_vertex->distance_from_source - e->terminal_vertex->distance_from_source;
   }
 }
 
-void MTPGraph::find_shortest_path(Vertex **_front, Vertex **_new_front) {
-  Vertex **tmp_front;
-  int tmp_front_size;
-  Vertex *v, *tv;
-  scalar_t d;
-
+void MTPGraph::force_positive_work_lengths() {
 #ifdef VERBOSE
   scalar_t residual_error = 0.0;
 #endif
   for(int n = 0; n < _nb_vertices; n++) {
-    for(Edge *e = vertices[n].root_edge; e; e = e->next) {
+    for(Edge *e = _vertices[n].root_edge; e; e = e->next) {
       if(e->work_length < 0) {
 #ifdef VERBOSE
         residual_error -= e->work_length;
@@ -172,12 +184,20 @@ void MTPGraph::find_shortest_path(Vertex **_front, Vertex **_new_front) {
 #ifdef VERBOSE
   cerr << "residual_error " << residual_error << endl;
 #endif
+}
+
+// This method does not change the edge occupation. It update
+// distance_from_source and best_pred_edge_to_source.
+void MTPGraph::find_shortest_path(Vertex **_front, Vertex **_new_front) {
+  Vertex **tmp_front;
+  int tmp_front_size;
+  Vertex *v, *tv;
+  scalar_t d;
 
   for(int v = 0; v < _nb_vertices; v++) {
-    vertices[v].distance_from_source = FLT_MAX;
-    vertices[v].pred_vertex = 0;
-    vertices[v].pred_edge = 0;
-    vertices[v].iteration = 0;
+    _vertices[v].distance_from_source = FLT_MAX;
+    _vertices[v].best_pred_edge_to_source = 0;
+    _vertices[v].iteration = 0;
   }
 
   int iteration = 0;
@@ -196,8 +216,7 @@ void MTPGraph::find_shortest_path(Vertex **_front, Vertex **_new_front) {
         tv = e->terminal_vertex;
         if(d < tv->distance_from_source) {
           tv->distance_from_source = d;
-          tv->pred_vertex = v;
-          tv->pred_edge = e;
+          tv->best_pred_edge_to_source = e;
           if(tv->iteration < iteration) {
             _new_front[_new_front_size++] = tv;
             tv->iteration = iteration;
@@ -218,46 +237,58 @@ void MTPGraph::find_shortest_path(Vertex **_front, Vertex **_new_front) {
 
 void MTPGraph::find_best_paths(scalar_t *lengths, int *result_edge_occupation) {
   scalar_t total_length;
+  Vertex *v;
+  Edge *e;
 
   for(int e = 0; e < _nb_edges; e++) {
-    edges[e].length = lengths[e];
+    _edges[e].length = lengths[e];
+    _edges[e].work_length = _edges[e].length;
   }
 
-  initialize_work_lengths();
+  // We use one iteration of find_shortest_path simply to propagate
+  // the distance to make all the edge lengths positive.
+  find_shortest_path(_front, _new_front);
+  update_work_lengths();
+
+  // #warning
+  // initialize_work_lengths_with_min();
 
   do {
-    total_length = 0.0;
+    force_positive_work_lengths();
     find_shortest_path(_front, _new_front);
-    update_work_length();
+    update_work_lengths();
 
-    // Do we reach the _sink?
-    if(_sink->pred_edge) {
+    total_length = 0.0;
 
+    // Do we reach the _sink?
+    if(_sink->best_pred_edge_to_source) {
       // If yes, compute the length of the best path
-      for(Vertex *v = _sink; v->pred_edge; v = v->pred_vertex) {
-        total_length += v->pred_edge->length;
+      v = _sink;
+      while(v->best_pred_edge_to_source) {
+        total_length += v->best_pred_edge_to_source->length;
+        v = v->best_pred_edge_to_source->origin_vertex;
       }
-
       // If that length is negative
       if(total_length < 0.0) {
+#ifdef VERBOSE
+        cout << "Found a path of length " << total_length << endl;
+#endif
         // Invert all the edges along the best path
-        for(Vertex *v = _sink; v->pred_edge; v = v->pred_vertex) {
-          Edge *e = v->pred_edge;
-          e->terminal_vertex = v->pred_vertex;
+        v = _sink;
+        while(v->best_pred_edge_to_source) {
+          e = v->best_pred_edge_to_source;
+          v = e->origin_vertex;
+          e->revert();
           e->occupied = 1 - e->occupied;
-          e->length = - e->length;
-          e->work_length = - e->work_length;
-          v->pred_vertex->del_edge(e);
-          v->add_edge(e);
         }
       }
     }
+
   } while(total_length < 0.0);
 
-  for(int n = 0; n < _nb_vertices; n++) {
-    Vertex *v = &vertices[n];
-    for(Edge *e = v->root_edge; e; e = e->next) {
-      result_edge_occupation[e->id] = e->occupied;
-    }
+  for(int k = 0; k < _nb_edges; k++) {
+    Edge *e = _edges + k;
+    if(e->occupied) { e->revert(); }
+    result_edge_occupation[k] = e->occupied;
   }
 }