Handle diagrams with a single point

4 files changed, 12 insertions, 3 deletions

diff --git a/src/Bottleneck_distance/include/gudhi/Bottleneck.h b/src/Bottleneck_distance/include/gudhi/Bottleneck.h
index ad437710..c916898d 100644
--- a/src/Bottleneck_distance/include/gudhi/Bottleneck.h
+++ b/src/Bottleneck_distance/include/gudhi/Bottleneck.h
@@ -36,7 +36,11 @@ namespace persistence_diagram {
 inline double bottleneck_distance_approx(Persistence_graph& g, double e) {
   double b_lower_bound = 0.;
   double b_upper_bound = g.max_dist_to_diagonal();
-  const double alpha = std::pow(g.size(), 1. / 5.);
+  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 04c7c118..33f03b9c 100644
--- a/src/Bottleneck_distance/include/gudhi/Persistence_graph.h
+++ b/src/Bottleneck_distance/include/gudhi/Persistence_graph.h
@@ -45,7 +45,7 @@ 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;
diff --git a/src/Bottleneck_distance/test/bottleneck_unit_test.cpp b/src/Bottleneck_distance/test/bottleneck_unit_test.cpp
index 2c520045..44141baa 100644
--- a/src/Bottleneck_distance/test/bottleneck_unit_test.cpp
+++ b/src/Bottleneck_distance/test/bottleneck_unit_test.cpp
@@ -153,4 +153,9 @@ BOOST_AUTO_TEST_CASE(global) {
   BOOST_CHECK(bottleneck_distance(v1, v2, 0.) <= upper_bound / 100.);
   BOOST_CHECK(bottleneck_distance(v1, v2, upper_bound / 10000.) <= upper_bound / 100. + upper_bound / 10000.);
   BOOST_CHECK(std::abs(bottleneck_distance(v1, v2, 0.) - bottleneck_distance(v1, v2, upper_bound / 10000.)) <= upper_bound / 10000.);
+
+  std::vector< std::pair<double, double> > empty;
+  std::vector< std::pair<double, double> > one = {{8, 10}};
+  BOOST_CHECK(bottleneck_distance(empty, empty) == 0);
+  BOOST_CHECK(bottleneck_distance(empty, one) == 1);
 }
diff --git a/src/python/doc/bottleneck_distance_user.rst b/src/python/doc/bottleneck_distance_user.rst
index 418dd11f..2c74c6dd 100644
--- a/src/python/doc/bottleneck_distance_user.rst
+++ b/src/python/doc/bottleneck_distance_user.rst
@@ -72,6 +72,6 @@ The output is:
 
 .. testoutput::
 
-    Bottleneck distance approximation = 0.81
+    Bottleneck distance approximation = 0.72
     Bottleneck distance value = 0.75