X-Git-Url: https://www.fleuret.org/cgi-bin/gitweb/gitweb.cgi?p=mtp.git;a=blobdiff_plain;f=mtp_graph.cc;h=2cbb33848a3589007528a6e3b1098357dbf3d3df;hp=e83c84869830b898af94965a9d35cf3815b657d0;hb=HEAD;hpb=a63e176f5b016f1d5a2a7b5101544430e5d3691e

diff --git a/mtp_graph.cc b/mtp_graph.cc
index e83c848..2cbb338 100644
--- a/mtp_graph.cc
+++ b/mtp_graph.cc
@@ -97,53 +97,46 @@ void Vertex::del_leaving_edge(Edge *e) {
 
 void Vertex::decrease_distance_in_heap(Vertex **heap) {
   Vertex **p, **h;
-  // There is some beauty in that
   h = heap_slot;
-  while(h > heap &&
-        (p = heap + (h - heap + 1) / 2 - 1,
-         (*p)->distance_from_source > (*h)->distance_from_source)) {
+  while(1) {
+    if(h <= heap) break;
+    p = heap + ((h - heap + 1) >> 1) - 1;
+    if((*p)->distance_from_source <= distance_from_source) break;
+    swap((*p)->heap_slot, heap_slot);
     swap(*p, *h);
-    swap((*p)->heap_slot, (*h)->heap_slot);
     h = p;
   }
 }
 
 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_bottom &&
-        (c2 = c1 + 1,
-         (*c1)->distance_from_source < (*h)->distance_from_source
-         ||
-         (c2 < heap_bottom && (*c2)->distance_from_source < (*h)->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;
+  while(1) {
+    c1 = heap + 2 * (h - heap) + 1;
+    if(c1 >= heap_bottom) break;
+    c2 = c1 + 1;
+    if((*c1)->distance_from_source < distance_from_source) {
+      if(c2 < heap_bottom && (*c2)->distance_from_source < (*c1)->distance_from_source) {
+        swap((*c2)->heap_slot, heap_slot);
+        swap(*c2, *h);
+        h = c2;
+      } else {
+        swap((*c1)->heap_slot, heap_slot);
+        swap(*c1, *h);
+        h = c1;
+      }
     } else {
-      swap(*c1, *h);
-      swap((*c1)->heap_slot, (*h)->heap_slot);
-      h = c1;
+      if(c2 < heap_bottom && (*c2)->distance_from_source < distance_from_source) {
+        swap((*c2)->heap_slot, heap_slot);
+        swap(*c2, *h);
+        h = c2;
+      } else break;
     }
   }
 }
 
 //////////////////////////////////////////////////////////////////////
 
-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;
-}
-
-//////////////////////////////////////////////////////////////////////
-
 MTPGraph::MTPGraph(int nb_vertices, int nb_edges,
                    int *vertex_from, int *vertex_to,
                    int source, int sink) {
@@ -159,10 +152,10 @@ MTPGraph::MTPGraph(int nb_vertices, int nb_edges,
   _sink = &_vertices[sink];
 
   for(int e = 0; e < nb_edges; e++) {
-    _vertices[vertex_from[e]].add_leaving_edge(_edges + e);
+    _vertices[vertex_from[e]].add_leaving_edge(&_edges[e]);
     _edges[e].occupied = 0;
-    _edges[e].origin_vertex = _vertices + vertex_from[e];
-    _edges[e].terminal_vertex = _vertices + vertex_to[e];
+    _edges[e].origin_vertex = &_vertices[vertex_from[e]];
+    _edges[e].terminal_vertex = &_vertices[vertex_to[e]];
   }
 
   for(int v = 0; v < _nb_vertices; v++) {
@@ -173,9 +166,7 @@ MTPGraph::MTPGraph(int nb_vertices, int nb_edges,
   paths = 0;
   nb_paths = 0;
 
-  compute_dp_ranks();
-  for(int v = 0; v < _nb_vertices; v++) { _dp_order[v] = &_vertices[v]; }
-  qsort(_dp_order, _nb_vertices, sizeof(Vertex *), compare_vertices_on_distance);
+  compute_dp_ordering();
 }
 
 MTPGraph::~MTPGraph() {
@@ -189,83 +180,9 @@ MTPGraph::~MTPGraph() {
 
 //////////////////////////////////////////////////////////////////////
 
-void MTPGraph::compute_dp_ranks() {
-  Vertex *v;
-  Edge *e;
-  int tv;
-
-  // 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.
-
-  int *nb_predecessors = new int[_nb_vertices];
-  int *without_predecessor = new int[_nb_vertices];
-  int *new_without_predecessor = new int[_nb_vertices];
-  int nb_without_predecessor, new_nb_without_predecessor;
-
-  for(int k = 0; k < _nb_vertices; k++) {
-    nb_predecessors[k] = 0;
-  }
-
-  for(int k = 0; k < _nb_vertices; k++) {
-    v = _vertices + k;
-    for(e = v->leaving_edge_list_root; e; e = e->next_leaving_edge) {
-      tv = int(e->terminal_vertex - _vertices);
-      nb_predecessors[tv]++;
-    }
-  }
-
-  nb_without_predecessor = 0;
-  for(int k = 0; k < _nb_vertices; k++) {
-    if(nb_predecessors[k] == 0) {
-      without_predecessor[nb_without_predecessor++] = k;
-    }
-  }
-
-  scalar_t rank = 1;
-  while(nb_without_predecessor > 0) {
-    new_nb_without_predecessor = 0;
-    for(int l = 0; l < nb_without_predecessor; l++) {
-      v = _vertices + without_predecessor[l];
-      v->distance_from_source = rank;
-      for(e = v->leaving_edge_list_root; e; e = e->next_leaving_edge) {
-        tv = int(e->terminal_vertex - _vertices);
-        nb_predecessors[tv]--;
-        ASSERT(nb_predecessors[tv] >= 0);
-        if(nb_predecessors[tv] == 0) {
-          new_without_predecessor[new_nb_without_predecessor++] = tv;
-        }
-      }
-    }
-
-    swap(without_predecessor, new_without_predecessor);
-    nb_without_predecessor = new_nb_without_predecessor;
-    rank++;
-  }
-
-  for(int k = 0; k < _nb_vertices; k++) {
-    if(nb_predecessors[k] > 0) {
-      cerr << __FILE__ << ": The graph is not a DAG." << endl;
-      abort();
-    }
-  }
-
-  delete[] nb_predecessors;
-  delete[] without_predecessor;
-  delete[] new_without_predecessor;
-}
-
-//////////////////////////////////////////////////////////////////////
-
 void MTPGraph::print(ostream *os) {
   for(int k = 0; k < _nb_edges; k++) {
-    Edge *e = _edges + k;
+    Edge *e = &_edges[k];
     (*os) << e->origin_vertex - _vertices
           << " -> "
           << e->terminal_vertex - _vertices
@@ -283,7 +200,7 @@ void MTPGraph::print_dot(ostream *os) {
   (*os) << "        " << _source - _vertices << " [peripheries=2];" << endl;
   (*os) << "        " << _sink - _vertices << " [peripheries=2];" << endl;
   for(int k = 0; k < _nb_edges; k++) {
-    Edge *e = _edges + k;
+    Edge *e = &_edges[k];
     (*os) << "        "
           << e->origin_vertex - _vertices
           << " -> "
@@ -301,7 +218,7 @@ void MTPGraph::print_dot(ostream *os) {
 
 void MTPGraph::update_positivized_lengths() {
   for(int k = 0; k < _nb_edges; k++) {
-    Edge *e = _edges + k;
+    Edge *e = &_edges[k];
     e->positivized_length +=
       e->origin_vertex->distance_from_source - e->terminal_vertex->distance_from_source;
   }
@@ -313,7 +230,7 @@ void MTPGraph::force_positivized_lengths() {
   scalar_t max_error = 0.0;
 #endif
   for(int k = 0; k < _nb_edges; k++) {
-    Edge *e = _edges + k;
+    Edge *e = &_edges[k];
 
     if(e->positivized_length < 0) {
 #ifdef VERBOSE
@@ -324,7 +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
 }
 
@@ -358,6 +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;
@@ -367,20 +285,20 @@ void MTPGraph::find_shortest_path() {
     _vertices[k].pred_edge_toward_source = 0;
   }
 
-  _heap_size = _nb_vertices;
+  heap_size = _nb_vertices;
   _source->distance_from_source = 0;
   _source->decrease_distance_in_heap(_heap);
 
-  do {
+  while(heap_size > 1) {
     // Get the closest to the source
     v = _heap[0];
 
     // Remove it from the heap (swap it with the last_slot in the heap, and
     // update the distance of that one)
-    _heap_size--;
-    last_slot = _heap + _heap_size;
+    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);
+    (*_heap)->increase_distance_in_heap(_heap, last_slot);
 
     // Now update the neighbors of the node currently closest to the
     // source
@@ -388,13 +306,13 @@ void MTPGraph::find_shortest_path() {
       d = v->distance_from_source + e->positivized_length;
       tv = e->terminal_vertex;
       if(d < tv->distance_from_source) {
-        ASSERT(tv->heap_slot - _heap < _heap_size);
+        ASSERT(tv->heap_slot < last_slot);
         tv->distance_from_source = d;
         tv->pred_edge_toward_source = e;
         tv->decrease_distance_in_heap(_heap);
       }
     }
-  } while(_heap_size > 0);
+  }
 }
 
 void MTPGraph::find_best_paths(scalar_t *lengths) {
@@ -456,12 +374,12 @@ void MTPGraph::find_best_paths(scalar_t *lengths) {
   // Put back the graph in its original state (i.e. invert edges which
   // have been inverted in the process)
   for(int k = 0; k < _nb_edges; k++) {
-    e = _edges + k;
+    e = &_edges[k];
     if(e->occupied) { e->invert(); }
   }
 }
 
-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;
 
@@ -478,7 +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
@@ -486,13 +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;
   }
 
@@ -504,9 +421,75 @@ int MTPGraph::retrieve_one_path(Edge *e, Path *path) {
   return l;
 }
 
+//////////////////////////////////////////////////////////////////////
+
+void MTPGraph::compute_dp_ordering() {
+  Vertex *v;
+  Edge *e;
+  int ntv;
+
+  // 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];
+
+  Vertex **already_processed = _dp_order, **front = _dp_order, **new_front = _dp_order;
+
+  for(int k = 0; k < _nb_vertices; k++) {
+    nb_predecessors[k] = 0;
+  }
+
+  for(int k = 0; k < _nb_vertices; k++) {
+    v = &_vertices[k];
+    for(e = v->leaving_edge_list_root; e; e = e->next_leaving_edge) {
+      ntv = int(e->terminal_vertex - _vertices);
+      nb_predecessors[ntv]++;
+    }
+  }
+
+  for(int k = 0; k < _nb_vertices; k++) {
+    if(nb_predecessors[k] == 0) {
+      *(front++) = _vertices + k;
+    }
+  }
+
+  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++);
+      for(e = v->leaving_edge_list_root; e; e = e->next_leaving_edge) {
+        ntv = int(e->terminal_vertex - _vertices);
+        nb_predecessors[ntv]--;
+        ASSERT(nb_predecessors[ntv] >= 0);
+        if(nb_predecessors[ntv] == 0) {
+          *(new_front++) = e->terminal_vertex;
+        }
+      }
+    }
+    front = new_front;
+  }
+
+  if(already_processed < _dp_order + _nb_vertices) {
+    cerr << __FILE__ << ": The graph is not a DAG." << endl;
+    abort();
+  }
+
+  delete[] nb_predecessors;
+}
+
+//////////////////////////////////////////////////////////////////////
+
 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;
@@ -517,14 +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;
 }