Fix assortativity for undirected graphs (ticket #52)

src/graph/correlations/graph_assortativity.hh

@@ -21,6 +21,7 @@
 #include <tr1/unordered_set>
 #include "shared_map.hh"
 #include "histogram.hh"
+#include "graph_util.hh"
 
 namespace graph_tool
 {
@@ -37,11 +38,14 @@ struct get_assortativity_coefficient
                     double& r_err) const
     {
         const Graph& g = *gp;
-        size_t n_edges = 0;
-        int e_kk = 0;
-        tr1::unordered_map<double,int> a, b;
-        SharedMap<tr1::unordered_map<double,int> > sa(a), sb(b);
-
+        typedef typename mpl::if_<typename is_directed::apply<Graph>::type,
+                                  size_t, double>::type count_t;
+
+        count_t c = (is_directed::apply<Graph>::type::value) ? 1.0 : 0.5;
+        count_t n_edges = 0;
+        count_t e_kk = 0;
+        tr1::unordered_map<double,count_t> a, b;
+        SharedMap<tr1::unordered_map<double,count_t> > sa(a), sb(b);
         int i, N = num_vertices(g);
         #pragma omp parallel for default(shared) private(i) firstprivate(sa,sb)\
             schedule(dynamic) reduction(+:e_kk, n_edges)
@@ -56,11 +60,11 @@ struct get_assortativity_coefficient
             for (tie(e,e_end) = out_edges(v, g); e != e_end; ++e)
             {
                 double k2 = deg(target(*e, g), g);
-                sa[k1]++;
-                sb[k2]++;
                 if (k1 == k2)
-                    e_kk++;
-                n_edges++;
+                    e_kk += c;
+                sa[k1] += c;
+                sb[k2] += c;
+                n_edges += c;
             }
         }
 
@@ -98,7 +102,7 @@ struct get_assortativity_coefficient
                     tl1 -= 1;
                 tl1 /= n_edges - 1;
                 double rl = (tl1 - tl2)/(1.0 - tl2);
-                err += (r-rl)*(r-rl);
+                err += (r-rl)*(r-rl)*c;
             }
         }
         r_err = sqrt(err);
@@ -115,10 +119,15 @@ struct get_scalar_assortativity_coefficient
                     double& r_err) const
     {
         const Graph& g = *gp;
-        size_t n_edges = 0;
+
+        typedef typename mpl::if_<typename is_directed::apply<Graph>::type,
+                                  size_t, double>::type count_t;
+
+        count_t c = (is_directed::apply<Graph>::type::value) ? 1.0 : 0.5;
+        count_t n_edges = 0;
         double e_xy = 0.0;
-        tr1::unordered_map<double,int> a, b;
-        SharedMap<tr1::unordered_map<double,int> > sa(a), sb(b);
+        tr1::unordered_map<double,count_t> a, b;
+        SharedMap<tr1::unordered_map<double,count_t> > sa(a), sb(b);
 
         int i, N = num_vertices(g);
         #pragma omp parallel for default(shared) private(i) firstprivate(sa,sb)\
@@ -134,10 +143,10 @@ struct get_scalar_assortativity_coefficient
             for (tie(e,e_end) = out_edges(v, g); e != e_end; ++e)
             {
                 double k2 = deg(target(*e,g),g);
-                sa[k1]++;
-                sb[k2]++;
-                e_xy += k1*k2;
-                n_edges++;
+                sa[k1] += c;
+                sb[k2] += c;
+                e_xy += k1*k2*c;
+                n_edges += c;
             }
         }
 
@@ -187,7 +196,7 @@ struct get_scalar_assortativity_coefficient
                     rl = (t1l - avg_al*avg_bl)/(dal*dbl);
                 else
                     rl = (t1l - avg_al*avg_bl);
-                err += (r-rl)*(r-rl);
+                err += (r-rl)*(r-rl)*c;
             }
         }
         r_err = sqrt(err);

src/graph/graph_bind.cc

@@ -337,6 +337,7 @@ BOOST_PYTHON_MODULE(libgraph_tool_core)
     variant_from_python<GraphInterface::degree_t>();
     to_python_converter<pair<string,bool>, pair_to_tuple<string,bool> >();
     to_python_converter<pair<size_t,size_t>, pair_to_tuple<size_t,size_t> >();
+    to_python_converter<pair<double,double>, pair_to_tuple<double,double> >();
     pair_from_tuple<double,double>();
     pair_from_tuple<size_t,size_t>();
 #ifdef HAVE_SCIPY

src/graph/graph_util.hh

@@ -35,6 +35,23 @@ namespace graph_tool
 {
 using namespace boost;
 
+//
+// Metaprogramming
+// ===============
+
+// useful metafunction to determine whether a graph is directed or not
+
+struct is_directed
+{
+    template <class Graph>
+    struct apply
+    {
+        typedef is_convertible<typename graph_traits<Graph>::directed_category,
+                               directed_tag> type;
+    };
+};
+
+
 // This will count "by hand" the number of vertices on a graph. Always O(V).
 struct HardNumVertices
 {