From a53afa3f85b63218dc8d95ca42d83d8f07c76c1e Mon Sep 17 00:00:00 2001
From: Jeremy Siek <jeremy.siek@gmail.com>
Date: Thu, 16 Aug 2001 18:57:48 +0000
Subject: [PATCH] made condensation graph separate

[SVN r10879]
---
 .../boost/graph/create_condensation_graph.hpp | 74 +++++++++++++++++++
 include/boost/graph/transitive_closure.hpp    | 30 ++------
 2 files changed, 81 insertions(+), 23 deletions(-)
 create mode 100644 include/boost/graph/create_condensation_graph.hpp

diff --git a/include/boost/graph/create_condensation_graph.hpp b/include/boost/graph/create_condensation_graph.hpp
new file mode 100644
index 00000000..10ceed68
--- /dev/null
+++ b/include/boost/graph/create_condensation_graph.hpp
@@ -0,0 +1,74 @@
+#ifndef BOOST_CREATE_CONDENSATION_GRAPH_HPP
+#define BOOST_CREATE_CONDENSATION_GRAPH_HPP
+
+#include <boost/graph/graph_traits.hpp>
+#include <boost/property_map.hpp>
+
+namespace boost {
+
+  template <typename Graph, typename ComponentLists, 
+    typename ComponentNumberMap,
+    typename CondensationGraph, typename EdgeMultiplicityMap>
+  void create_condensation_graph(const Graph& g, 
+                                 const ComponentLists& components,
+                                 ComponentNumberMap component_number,
+                                 CondensationGraph& cg,
+                                 EdgeMultiplicityMap edge_mult_map)
+  {
+    typedef typename graph_traits<Graph>::vertex_descriptor vertex;
+    typedef typename graph_traits<Graph>::vertices_size_type size_type;
+    typedef typename graph_traits<CondensationGraph>::vertex_descriptor 
+      cg_vertex;
+    std::vector<cg_vertex> to_cg_vertex(components.size());
+    for (size_type s = 0; s < components.size(); ++s)
+      to_cg_vertex[s] = add_vertex(cg);
+
+    for (size_type si = 0; si < components.size(); ++si) {
+      cg_vertex s = to_cg_vertex[si];
+      std::vector<cg_vertex> adj;
+      for (size_type i = 0; i < components[si].size(); ++i) {
+        vertex u = components[s][i];
+        typename graph_traits<Graph>::adjacency_iterator v, v_end;
+        for (tie(v, v_end) = adjacent_vertices(u, g); v != v_end; ++v) {
+          cg_vertex t = to_cg_vertex[component_number[*v]];
+          if (s != t) // Avoid loops in the condensation graph
+            adj.push_back(t);
+        }
+      }
+      std::sort(adj.begin(), adj.end());
+      if (! adj.empty()) {
+        size_type i = 0;
+        cg_vertex t = adj[i];
+        typename graph_traits<CondensationGraph>::edge_descriptor e;
+        bool inserted;
+        tie(e, inserted) = add_edge(s, t, cg);
+        put(edge_mult_map, e, 1);
+        ++i;
+        while (i < adj.size()) {
+          if (adj[i] == t)
+            put(edge_mult_map, e, get(edge_mult_map, e) + 1);
+          else {
+            t = adj[i];
+            tie(e, inserted) = add_edge(s, t, cg);
+            put(edge_mult_map, e, 1);
+          }
+          ++i;
+        }
+      }
+    }
+  }
+  
+  template <typename Graph, typename ComponentLists, 
+    typename ComponentNumberMap, typename CondensationGraph>
+  void create_condensation_graph(const Graph& g, 
+                                 const ComponentLists& components,
+                                 ComponentNumberMap component_number,
+                                 CondensationGraph& cg)
+  {
+    create_condensation_graph(g, components, component_number, cg, 
+                              dummy_property_map());
+  }
+
+} // namespace boost
+
+#endif // BOOST_CREATE_CONDENSATION_GRAPH_HPP
diff --git a/include/boost/graph/transitive_closure.hpp b/include/boost/graph/transitive_closure.hpp
index 34cbf1cf..19389a1a 100644
--- a/include/boost/graph/transitive_closure.hpp
+++ b/include/boost/graph/transitive_closure.hpp
@@ -15,6 +15,7 @@
 #include <boost/graph/vector_as_graph.hpp>
 #include <boost/graph/strong_components.hpp>
 #include <boost/graph/topological_sort.hpp>
+#include <boost/graph/create_condensation_graph.hpp>
 
 // For a description of the implementation see ../doc/transitive_closure.pdf.
 
@@ -74,6 +75,7 @@ namespace boost {
     typedef typename property_traits<VertexIndexMap>::value_type size_type;
     typedef typename graph_traits<Graph>::adjacency_iterator 
       adjacency_iterator;
+    typedef size_type cg_vertex;
 
     function_requires< VertexListGraphConcept<Graph> >();
     function_requires< AdjacencyGraphConcept<Graph> >();
@@ -81,44 +83,26 @@ namespace boost {
     function_requires< EdgeMutableGraphConcept<GraphTC> >();
     function_requires< ReadablePropertyMapConcept<VertexIndexMap, vertex> >();
 
-    // Compute strongly connected components of the graph
-    typedef size_type cg_vertex;
     std::vector<cg_vertex> component_number_vec(num_vertices(g));
     iterator_property_map<cg_vertex*, VertexIndexMap> 
       component_number(&component_number_vec[0], index_map);
 
     int num_scc = strong_components(g, component_number,
       vertex_index_map(index_map));
+
     std::vector< std::vector<vertex> > components;
     build_component_lists(g, num_scc, component_number, components);
 
-    // Construct the condensation graph   
     typedef std::vector< std::vector<cg_vertex> > CG_t;
-    CG_t CG(num_scc);
-    for (cg_vertex s = 0; s < components.size(); ++s) {
-      std::vector<cg_vertex> adj;
-      for (size_type i = 0; i < components[s].size(); ++i) {
-        vertex u = components[s][i];
-        adjacency_iterator v, v_end;
-        for (tie(v, v_end) = adjacent_vertices(u, g); v != v_end; ++v) {
-          cg_vertex t = component_number[*v];
-          if (s != t) // Avoid loops in the condensation graph
-            adj.push_back(t);
-        }
-      }
-      std::sort(adj.begin(), adj.end());
-      std::vector<cg_vertex>::iterator
-	di = std::unique(adj.begin(), adj.end());
-      if (di != adj.end())
-        adj.erase(di, adj.end());        
-      CG[s] = adj;
-    }
+    CG_t CG;
+    create_condensation_graph(g, components, component_number, CG);
 
-    // topological sort the condensation graph
     std::vector<cg_vertex> topo_order;
     std::vector<cg_vertex> topo_number(num_vertices(CG));
+
     topological_sort(CG, std::back_inserter(topo_order), 
       vertex_index_map(identity_property_map()));
+
     std::reverse(topo_order.begin(), topo_order.end());
     size_type n = 0;
     for (std::vector<cg_vertex>::iterator i = topo_order.begin();