2 files changed, 15 insertions, 11 deletions
diff --git a/src/Bottleneck_distance/include/gudhi/Bottleneck.h b/src/Bottleneck_distance/include/gudhi/Bottleneck.h
index e466828a..c916898d 100644
--- a/src/Bottleneck_distance/include/gudhi/Bottleneck.h
+++ b/src/Bottleneck_distance/include/gudhi/Bottleneck.h
@@ -35,8 +35,12 @@ namespace persistence_diagram {
 
 inline double bottleneck_distance_approx(Persistence_graph& g, double e) {
   double b_lower_bound = 0.;
-  double b_upper_bound = g.diameter_bound();
-  const double alpha = std::pow(g.size(), 1. / 5.);
+  double b_upper_bound = g.max_dist_to_diagonal();
+  int siz = g.size();
+  if (siz <= 1)
+    // The value of alpha would be wrong in this case
+    return b_upper_bound;
+  const double alpha = std::pow(siz, 1. / 5.);
   Graph_matching m(g);
   Graph_matching biggest_unperfect(g);
   while (b_upper_bound - b_lower_bound > 2 * e) {
diff --git a/src/Bottleneck_distance/include/gudhi/Persistence_graph.h b/src/Bottleneck_distance/include/gudhi/Persistence_graph.h
index e1e3522e..33f03b9c 100644
--- a/src/Bottleneck_distance/include/gudhi/Persistence_graph.h
+++ b/src/Bottleneck_distance/include/gudhi/Persistence_graph.h
@@ -45,14 +45,14 @@ class Persistence_graph {
   int corresponding_point_in_v(int u_point_index) const;
   /** \internal \brief Given a point from U and a point from V, returns the distance between those points. */
   double distance(int u_point_index, int v_point_index) const;
-  /** \internal \brief Returns size = |U| = |V|. */
+  /** \internal \brief Returns size = |U| + |V|. */
   int size() const;
   /** \internal \brief Is there as many infinite points (alive components) in both diagrams ? */
   double bottleneck_alive() const;
   /** \internal \brief Returns the O(n^2) sorted distances between the points. */
   std::vector<double> sorted_distances() const;
-  /** \internal \brief Returns an upper bound for the diameter of the convex hull of all non infinite points */
-  double diameter_bound() const;
+  /** \internal \brief Returns an upper bound for the bottleneck distance of the finite points. */
+  double max_dist_to_diagonal() const;
   /** \internal \brief Returns the corresponding internal point */
   Internal_point get_u_point(int u_point_index) const;
   /** \internal \brief Returns the corresponding internal point */
@@ -160,13 +160,13 @@ inline Internal_point Persistence_graph::get_v_point(int v_point_index) const {
   return Internal_point(m, m, v_point_index);
 }
 
-inline double Persistence_graph::diameter_bound() const {
+inline double Persistence_graph::max_dist_to_diagonal() const {
   double max = 0.;
-  for (auto it = u.cbegin(); it != u.cend(); it++)
-    max = (std::max)(max, it->y());
-  for (auto it = v.cbegin(); it != v.cend(); it++)
-    max = (std::max)(max, it->y());
-  return max;
+  for (auto& p : u)
+    max = (std::max)(max, p.y() - p.x());
+  for (auto& p : v)
+    max = (std::max)(max, p.y() - p.x());
+  return max / 2;
 }
 
 }  // namespace persistence_diagram