diff --git a/.gitattributes b/.gitattributes
index 38345480ef1..0f59509c4d2 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -4016,6 +4016,7 @@ Surface_mesh_segmentation/example/Surface_mesh_segmentation/segmentation_example
 Surface_mesh_segmentation/example/Surface_mesh_segmentation/simple_example.cpp -text
 Surface_mesh_segmentation/include/CGAL/Surface_mesh_segmentation.h -text
 Surface_mesh_segmentation/include/CGAL/internal/Surface_mesh_segmentation/AABB_traversal_traits.h -text
+Surface_mesh_segmentation/include/CGAL/internal/Surface_mesh_segmentation/Alpha_expansion_graph_cut.h -text
 Surface_mesh_segmentation/include/CGAL/internal/Surface_mesh_segmentation/Expectation_maximization.h -text
 Surface_mesh_segmentation/include/CGAL/internal/Surface_mesh_segmentation/K_means_clustering.h -text
 Surface_mesh_segmentation/package_info/Surface_mesh_segmentation/copyright -text
diff --git a/Surface_mesh_segmentation/include/CGAL/Surface_mesh_segmentation.h b/Surface_mesh_segmentation/include/CGAL/Surface_mesh_segmentation.h
index 3eb0048be08..64e2fce0692 100644
--- a/Surface_mesh_segmentation/include/CGAL/Surface_mesh_segmentation.h
+++ b/Surface_mesh_segmentation/include/CGAL/Surface_mesh_segmentation.h
@@ -16,6 +16,7 @@
 
 #include <CGAL/internal/Surface_mesh_segmentation/Expectation_maximization.h>
 #include <CGAL/internal/Surface_mesh_segmentation/K_means_clustering.h>
+#include <CGAL/internal/Surface_mesh_segmentation/Alpha_expansion_graph_cut.h>
 
 //AF: This files does not use Simple_cartesian
 //IOY: Yes, not sure where it came from (with update may be),  I am going to ask about it.
@@ -44,7 +45,7 @@
 #define CGAL_ANGLE_ST_DEV_DIVIDER 3.0
 
 //IOY: these are going to be removed at the end (no CGAL_ pref)
-//#define ACTIVATE_SEGMENTATION_DEBUG
+#define ACTIVATE_SEGMENTATION_DEBUG
 #ifdef ACTIVATE_SEGMENTATION_DEBUG
 #define SEG_DEBUG(x) x;
 #else
@@ -136,11 +137,11 @@ public:
   double calculate_sdf_value_of_facet (const Facet_handle& facet,
                                        const Tree& tree) const;
   template <class Query>
-  boost::optional<double> cast_and_return_minimum(const Query& ray,
+  boost::tuple<bool, bool, double> cast_and_return_minimum(const Query& ray,
       const Tree& tree, const Facet_handle& facet) const;
   template <class Query>
-  boost::optional<double> cast_and_return_minimum_use_closest(const Query& ray,
-      const Tree& tree, const Facet_handle& facet) const;
+  boost::tuple<bool, bool, double> cast_and_return_minimum_use_closest(
+    const Query& ray, const Tree& tree, const Facet_handle& facet) const;
 
   double calculate_sdf_value_from_rays (std::vector<double>& ray_distances,
                                         std::vector<double>& ray_weights) const;
@@ -165,6 +166,7 @@ public:
   void apply_GMM_fitting();
   void apply_K_means_clustering();
   void apply_GMM_fitting_with_K_means_init();
+  void apply_graph_cut();
 
   void write_sdf_values(const char* file_name);
   void read_sdf_values(const char* file_name);
@@ -192,10 +194,12 @@ inline Surface_mesh_segmentation<Polyhedron>::Surface_mesh_segmentation(
   calculate_sdf_values();
   SEG_DEBUG(std::cout << t.time() << std::endl)
 #endif
-  //apply_GMM_fitting();
+  //
   //write_sdf_values("sdf_values_sample_dino_ws.txt");
-  //read_sdf_values("sdf_values_sample_camel.txt");
-  //calculate_dihedral_angles();
+  //read_sdf_values("sdf_values_sample_elephant.txt");
+  //apply_GMM_fitting();
+  apply_graph_cut();
+
 }
 
 template <class Polyhedron>
@@ -207,7 +211,6 @@ inline void Surface_mesh_segmentation<Polyhedron>::calculate_sdf_values()
       facet_it != mesh->facets_end(); ++facet_it) {
     CGAL_precondition(facet_it->is_triangle()); //Mesh should contain triangles.
 
-    //SL: cone angle and number of rays should be parameters.
     double sdf = calculate_sdf_value_of_facet(facet_it, tree);
     sdf_values.insert(std::pair<Facet_handle, double>(facet_it, sdf));
   }
@@ -244,7 +247,7 @@ Surface_mesh_segmentation<Polyhedron>::calculate_sdf_value_of_facet(
   v1 = v1 / sqrt(v1.squared_length());
   v2 = v2 / sqrt(v2.squared_length());
 
-  arrange_center_orientation(plane, normal, center);
+  //arrange_center_orientation(plane, normal, center);
 
   int ray_count = number_of_rays_sqrt * number_of_rays_sqrt;
 
@@ -265,22 +268,25 @@ Surface_mesh_segmentation<Polyhedron>::calculate_sdf_value_of_facet(
 #endif
   for(Disk_samples_list::const_iterator sample_it = disk_samples.begin();
       sample_it != disk_samples.end(); ++sample_it) {
-    boost::optional<double> min_distance;
+    bool is_intersected, intersection_is_acute;
+    double min_distance;
     Vector disk_vector = v1 * sample_it->first + v2 * sample_it->second;
     Vector ray_direction = normal + disk_vector;
 
 #ifdef SHOOT_ONLY_RAYS
     Ray ray(center, ray_direction);
-    min_distance = cast_and_return_minimum(ray, tree, facet);
-    if(!min_distance) {
+    boost::tie(is_intersected, intersection_is_acute,
+               min_distance) = cast_and_return_minimum(ray, tree, facet);
+    if(!intersection_is_acute) {
       continue;
     }
 #else
     // at first cast ray
     if(!segment_distance) {
       Ray ray(center, ray_direction);
-      min_distance = cast_and_return_minimum(ray, tree, facet);
-      if(!min_distance) {
+      boost::tie(is_intersected, intersection_is_acute,
+                 min_distance) = cast_and_return_minimum(ray, tree, facet);
+      if(!intersection_is_acute) {
         continue;
       }
       segment_distance = min_distance; //first assignment of the segment_distance
@@ -289,43 +295,54 @@ Surface_mesh_segmentation<Polyhedron>::calculate_sdf_value_of_facet(
 
       ray_direction = ray_direction * (*segment_distance * multiplier_for_segment);
       Segment segment(center, CGAL::operator+(center, ray_direction));
-      min_distance = cast_and_return_minimum(segment, tree, facet);
-      if(!min_distance) {
+      boost::tie(is_intersected, intersection_is_acute,
+                 min_distance) = cast_and_return_minimum(segment, tree, facet);
+      if(!is_intersected) {
         //continue; // for utopia case - just continue on miss
         ++miss_counter;
+        //Ray ray(segment.target(), ray_direction);
         Ray ray(segment.target(), ray_direction);
-        min_distance = cast_and_return_minimum(ray, tree, facet);
-        if(!min_distance) {
+        boost::tie(is_intersected, intersection_is_acute,
+                   min_distance) = cast_and_return_minimum(ray, tree, facet);
+        if(!intersection_is_acute) {
           continue;
         }
+        min_distance += CGAL::sqrt(
+                          segment.squared_length()); // since we our source is segment.target()
+      } else if(!intersection_is_acute) {
+        continue;
       }
+
       if(use_minimum_segment) {
-        if(*min_distance <
+        if(min_distance <
             *segment_distance) { // update segment_distance (minimum / maximum)
-          *segment_distance = *min_distance;
+          *segment_distance = min_distance;
         }
       } else {
-        if(*min_distance >
+        if(min_distance >
             *segment_distance) { // update segment_distance (minimum / maximum)
-          *segment_distance = *min_distance;
+          *segment_distance = min_distance;
         }
       }
     }
 #endif
     ray_weights.push_back(sample_it->third);
-    ray_distances.push_back(*min_distance);
+    ray_distances.push_back(min_distance);
   }
   return calculate_sdf_value_from_rays_with_trimmed_mean(ray_distances,
          ray_weights);
 }
 
+// just for Ray and Segment
+
 template <class Polyhedron>
-template <class Query> // just for Ray and Segment
-boost::optional<double>
+template <class Query>
+boost::tuple<bool, bool, double>
 Surface_mesh_segmentation<Polyhedron>::cast_and_return_minimum(
   const Query& query, const Tree& tree, const Facet_handle& facet) const
 {
-  boost::optional<double> min_distance;
+  boost::tuple<bool, bool, double> min_distance = boost::make_tuple(false, false,
+      0);
   std::list<Object_and_primitive_id> intersections;
 #if 1
   //SL: the difference with all_intersections is that in the traversal traits, we do do_intersect before calling intersection.
@@ -359,13 +376,14 @@ Surface_mesh_segmentation<Polyhedron>::cast_and_return_minimum(
 
     Vector i_ray = (query.source() - *i_point);
     double new_distance = i_ray.squared_length();
-    if(!min_distance || new_distance < min_distance) {
-      min_distance = new_distance;
+    if(!min_distance.get<0>() || new_distance < min_distance.get<2>()) {
+      min_distance.get<2>() = new_distance;
+      min_distance.get<0>() = true;
       min_id = id;
       min_i_ray = i_ray;
     }
   }
-  if(!min_distance) {
+  if(!min_distance.get<0>()) {
     return min_distance;
   }
 
@@ -376,14 +394,16 @@ Surface_mesh_segmentation<Polyhedron>::cast_and_return_minimum(
 
   if(CGAL::angle(CGAL::ORIGIN + min_i_ray, Point(CGAL::ORIGIN),
                  CGAL::ORIGIN + min_normal) != CGAL::ACUTE) {
-    return boost::optional<double>();
+    return min_distance;
   }
-  return (*min_distance = sqrt(*min_distance));
+  min_distance.get<1>() = true; // founded intersection is acceptable.
+  min_distance.get<2>() = sqrt(min_distance.get<2>());
+  return min_distance;
 }
 
 template <class Polyhedron>
 template <class Query>
-boost::optional<double>
+boost::tuple<bool, bool, double>
 Surface_mesh_segmentation<Polyhedron>::cast_and_return_minimum_use_closest (
   const Query& ray, const Tree& tree,
   const Facet_handle& facet) const
@@ -391,7 +411,9 @@ Surface_mesh_segmentation<Polyhedron>::cast_and_return_minimum_use_closest (
   //static double dist = 0.1;
   //boost::optional<double> min_distance_2 = dist++;
   //return min_distance_2;
-  boost::optional<double> min_distance;
+
+  boost::tuple<bool, bool, double> min_distance = boost::make_tuple(false, false,
+      0);
 #if 1
   Closest_intersection_traits<typename Tree::AABB_traits, Query> traversal_traits;
   tree.traversal(ray, traversal_traits);
@@ -404,6 +426,7 @@ Surface_mesh_segmentation<Polyhedron>::cast_and_return_minimum_use_closest (
   if(!intersection) {
     return min_distance;
   }
+  min_distance.get<0>() = true; // intersection is found
 
   CGAL::Object object = intersection->first;
   Primitive_id min_id = intersection->second;
@@ -427,7 +450,9 @@ Surface_mesh_segmentation<Polyhedron>::cast_and_return_minimum_use_closest (
                  CGAL::ORIGIN + min_normal) != CGAL::ACUTE) {
     return min_distance;
   }
-  return (min_distance = sqrt(min_i_ray.squared_length()));
+  min_distance.get<1>() = true;
+  min_distance.get<2>() = sqrt(min_i_ray.squared_length());
+  return min_distance;
 }
 
 template <class Polyhedron>
@@ -873,7 +898,7 @@ inline void Surface_mesh_segmentation<Polyhedron>::apply_GMM_fitting()
   SEG_DEBUG(CGAL::Timer t)
   SEG_DEBUG(t.start())
   // apply em with 5 runs, number of runs might become a parameter.
-  internal::Expectation_maximization fitter(number_of_centers, sdf_vector, 5);
+  internal::Expectation_maximization fitter(number_of_centers, sdf_vector, 10);
   SEG_DEBUG(std::cout << t.time() << std::endl)
   std::vector<int> center_memberships;
   fitter.fill_with_center_ids(center_memberships);
@@ -930,6 +955,59 @@ Surface_mesh_segmentation<Polyhedron>::apply_GMM_fitting_with_K_means_init()
   }
 }
 
+template <class Polyhedron>
+void Surface_mesh_segmentation<Polyhedron>::apply_graph_cut()
+{
+  //assign an id for every facet (facet-id)
+  std::map<Facet_handle, int> facet_indices;
+  int index = 0;
+  for(Facet_iterator facet_it = mesh->facets_begin();
+      facet_it != mesh->facets_end();
+      ++facet_it, ++index) {
+    facet_indices.insert(std::pair<Facet_handle, int>(facet_it, index));
+  }
+  //edges and their weights. pair<int, int> stores facet-id pairs (see above) (may be using CGAL::Triple can be more suitable)
+  std::vector<std::pair<int, int> > edges;
+  std::vector<double> edge_weights;
+  for(Edge_iterator edge_it = mesh->edges_begin(); edge_it != mesh->edges_end();
+      ++edge_it) {
+    double angle = calculate_dihedral_angle_of_edge(edge_it);
+    int index_f1 = facet_indices[edge_it->facet()];
+    int index_f2 = facet_indices[edge_it->opposite()->facet()];
+    edges.push_back(std::pair<int, int>(index_f1, index_f2));
+    angle = -log(angle);
+    angle *= 15; //lambda, will be variable.
+    // we may also want to consider edge lengths, also penalize convex angles.
+    edge_weights.push_back(angle);
+  }
+  //apply gmm fitting
+  std::vector<double> sdf_vector;
+  sdf_vector.reserve(sdf_values.size());
+  for(typename Face_value_map::iterator pair_it = sdf_values.begin();
+      pair_it != sdf_values.end(); ++pair_it) {
+    sdf_vector.push_back(pair_it->second);
+  }
+  internal::Expectation_maximization fitter(number_of_centers, sdf_vector, 50);
+  //fill probability matrix.
+  std::vector<std::vector<double> > probability_matrix;
+  fitter.fill_with_minus_log_probabilities(probability_matrix);
+  std::vector<int> labels;
+  fitter.fill_with_center_ids(labels);
+
+  //apply graph cut
+  std::vector<int> center_ids;
+  internal::Alpha_expansion_graph_cut gc(edges, edge_weights, labels,
+                                         probability_matrix, center_ids);
+
+  std::vector<int>::iterator center_it = center_ids.begin();
+  centers.clear();
+  for(Facet_iterator facet_it = mesh->facets_begin();
+      facet_it != mesh->facets_end();
+      ++facet_it, ++center_it) {
+    centers.insert(std::pair<Facet_handle, int>(facet_it, (*center_it)));
+  }
+}
+
 //AF: it is not common in CGAL to have functions with a file name as argument
 //IOY: Yes, I am just using these read-write functions in development phase,
 // in order to not to compute sdf-values everytime program runs.
diff --git a/Surface_mesh_segmentation/include/CGAL/internal/Surface_mesh_segmentation/Alpha_expansion_graph_cut.h b/Surface_mesh_segmentation/include/CGAL/internal/Surface_mesh_segmentation/Alpha_expansion_graph_cut.h
new file mode 100644
index 00000000000..8cbee29b8a9
--- /dev/null
+++ b/Surface_mesh_segmentation/include/CGAL/internal/Surface_mesh_segmentation/Alpha_expansion_graph_cut.h
@@ -0,0 +1,141 @@
+#ifndef CGAL_ALPHA_EXPANSION_GRAPH_CUT_H
+#define CGAL_ALPHA_EXPANSION_GRAPH_CUT_H
+
+#include <CGAL/assertions.h>
+
+#include <boost/graph/adjacency_list.hpp>
+#include <boost/graph/boykov_kolmogorov_max_flow.hpp>
+#include <boost/math/distributions/normal.hpp>
+
+#include <iostream>
+#include <vector>
+
+namespace CGAL
+{
+namespace internal
+{
+
+class Alpha_expansion_graph_cut
+{
+public:
+  typedef boost::adjacency_list_traits<boost::vecS, boost::vecS, boost::directedS>
+  Adjacency_list_traits;
+
+  typedef boost::adjacency_list<boost::vecS, boost::vecS, boost::directedS,
+          // 4 vertex properties (nested)
+          //boost::no_property
+          boost::property<boost::vertex_index_t, int,
+          boost::property<boost::vertex_color_t, boost::default_color_type,
+          boost::property<boost::vertex_distance_t, double,
+          boost::property<boost::vertex_predecessor_t, Adjacency_list_traits::edge_descriptor >
+          > > >,
+          // 3 edge properties (nested)
+          boost::property<boost::edge_capacity_t, double,
+          boost::property<boost::edge_residual_capacity_t, double,
+          boost::property<boost::edge_reverse_t, Adjacency_list_traits::edge_descriptor> >
+          > > Graph;
+
+  typedef boost::graph_traits<Graph> Traits;
+  typedef boost::color_traits<boost::default_color_type> ColorTraits;
+
+  typedef Traits::vertex_descriptor Vertex_descriptor;
+  typedef Traits::edge_descriptor Edge_descriptor;
+  typedef Traits::vertex_iterator Vertex_iterator;
+  typedef Traits::edge_iterator Edge_iterator;
+
+  Alpha_expansion_graph_cut(std::vector<std::pair<int, int> >& edges,
+                            std::vector<double>& edge_weights, std::vector<int>& labels,
+                            std::vector<std::vector<double> >& probability_matrix,
+                            std::vector<int>& center_ids) {
+    //Graph graph(edges.begin(), edges.end(), vertex_weights.size(), edge_weights.size());
+    Graph graph;
+    Vertex_descriptor cluster_source = boost::add_vertex(graph);
+    Vertex_descriptor cluster_sink = boost::add_vertex(graph);
+    std::vector<Vertex_descriptor> inserted_vertices;
+    //inserted_vertices.reserve(vertex_weights.size());
+    for(std::size_t vertex_i = 0; vertex_i <  probability_matrix[0].size();
+        ++vertex_i) {
+      Vertex_descriptor new_vertex = boost::add_vertex(graph);
+      inserted_vertices.push_back(new_vertex);
+
+      Edge_descriptor source_e, source_e_rev, sink_e, sink_e_rev;
+      bool source_e_added, source_e_rev_added, sink_e_added, sink_e_rev_added;
+
+      tie(source_e, source_e_added) = boost::add_edge(cluster_source, new_vertex,
+                                      graph);
+      tie(source_e_rev, source_e_rev_added) = boost::add_edge(new_vertex,
+                                              cluster_source, graph);
+
+      tie(sink_e, sink_e_added) = boost::add_edge(new_vertex, cluster_sink, graph);
+      tie(sink_e_rev, sink_e_rev_added) = boost::add_edge(cluster_sink, new_vertex,
+                                          graph);
+
+      CGAL_assertion(source_e_added && source_e_rev_added &&  sink_e_added
+                     && sink_e_rev_added);
+
+      //put vertex capacities (to edges between itself and source & sink)
+      boost::put(boost::edge_capacity, graph, source_e,
+                 probability_matrix[0][vertex_i]);
+      boost::put(boost::edge_capacity, graph, source_e_rev, 0);
+      boost::put(boost::edge_capacity, graph, sink_e,
+                 probability_matrix[1][vertex_i]);
+      boost::put(boost::edge_capacity, graph, sink_e_rev, 0);
+      //map reverse edges
+      boost::put(boost::edge_reverse, graph, source_e, source_e_rev);
+      boost::put(boost::edge_reverse, graph, source_e_rev, source_e);
+      boost::put(boost::edge_reverse, graph, sink_e, sink_e_rev);
+      boost::put(boost::edge_reverse, graph, sink_e_rev, sink_e);
+    }
+    std::vector<double>::iterator weight_it = edge_weights.begin();
+    for(std::vector<std::pair<int, int> >::iterator edge_it = edges.begin();
+        edge_it != edges.end();
+        ++edge_it, ++weight_it) {
+      Vertex_descriptor v1 = inserted_vertices[edge_it->first];
+      Vertex_descriptor v2 = inserted_vertices[edge_it->second];
+
+      bool edge_added, edge_rev_added;
+      Edge_descriptor edge, edge_rev;
+      tie(edge, edge_added) = boost::add_edge(v1, v2, graph);
+      tie(edge_rev, edge_rev_added) = boost::add_edge(v2, v1, graph);
+
+      CGAL_assertion(edge_added && edge_rev_added);
+
+      //put edge capacities
+      if(labels[edge_it->first] == labels[edge_it->second]) {
+        boost::put(boost::edge_capacity, graph, edge,  *weight_it);
+        boost::put(boost::edge_capacity, graph, edge_rev,  *weight_it);
+      } else {
+        boost::put(boost::edge_capacity, graph, edge, *weight_it);
+        boost::put(boost::edge_capacity, graph, edge_rev, *weight_it);
+      }
+
+      //map reverse edges
+      boost::put(boost::edge_reverse, graph, edge, edge_rev);
+      boost::put(boost::edge_reverse, graph, edge_rev, edge);
+    }
+    double flow = boost::boykov_kolmogorov_max_flow(graph, cluster_source,
+                  cluster_sink);
+
+    for(std::vector<Vertex_descriptor>::iterator vertex_it =
+          inserted_vertices.begin();
+        vertex_it != inserted_vertices.end(); ++vertex_it) {
+      boost::default_color_type color = boost::get(boost::vertex_color, graph,
+                                        *vertex_it);
+      if(color == ColorTraits::black() ) { // in sink
+        center_ids.push_back(1);
+      } else {
+        center_ids.push_back(0);
+      }
+    }
+    std::cout << flow << std::endl;
+    //for(std::pair<Vertex_iterator, Vertex_iterator> pair_v = boost::vertices(graph);
+    //    pair_v.first != pair_v.second; ++(pair_v.first))
+    //{
+    //    if(cluster_source == (*pair_v.first) || cluster_sink == (*pair_v.first)) { continue; }
+    //
+    //}
+  }
+};
+}//namespace internal
+}//namespace CGAL
+#endif //CGAL_ALPHA_EXPANSION_GRAPH_CUT_H
\ No newline at end of file
diff --git a/Surface_mesh_segmentation/include/CGAL/internal/Surface_mesh_segmentation/Expectation_maximization.h b/Surface_mesh_segmentation/include/CGAL/internal/Surface_mesh_segmentation/Expectation_maximization.h
index 34ccdba1921..86f58f98965 100644
--- a/Surface_mesh_segmentation/include/CGAL/internal/Surface_mesh_segmentation/Expectation_maximization.h
+++ b/Surface_mesh_segmentation/include/CGAL/internal/Surface_mesh_segmentation/Expectation_maximization.h
@@ -19,7 +19,8 @@
 #define DEF_MAX_ITER  100
 #define DEF_THRESHOLD 1e-4
 #define USE_MATRIX    true
-//#define ACTIVATE_SEGMENTATION_EM_DEBUG
+
+#define ACTIVATE_SEGMENTATION_EM_DEBUG
 #ifdef ACTIVATE_SEGMENTATION_EM_DEBUG
 #define SEG_DEBUG(x) x;
 #else
@@ -111,7 +112,7 @@ public:
       int max_center = 0, center_counter = 0;
       for(std::vector<Gaussian_center>::iterator center_it = centers.begin();
           center_it != centers.end(); ++center_it, center_counter++) {
-        double likelihood = center_it->probability_with_coef(*point_it);
+        double likelihood = center_it->probability(*point_it);
         if(max_likelihood < likelihood) {
           max_likelihood = likelihood;
           max_center = center_counter;
@@ -120,6 +121,46 @@ public:
       data_centers.push_back(max_center);
     }
   }
+
+  void fill_with_minus_log_probabilities(std::vector<std::vector<double> >&
+                                         probabilities) {
+    double epsilon = 1e
+                     -8; // this epsilon should be consistent with epsilon in calculate_dihedral_angle_of_edge!
+    probabilities = std::vector<std::vector<double> >
+                    (centers.size(), std::vector<double>(points.size()));
+    for(std::size_t center_i = 0; center_i < centers.size(); ++center_i) {
+      double sum = 0.0;
+
+      for(std::size_t point_i = 0; point_i < points.size(); ++point_i) {
+        double probability = centers[center_i].probability(points[point_i]);
+        sum += probability;
+        probabilities[center_i][point_i] = probability;
+      }
+#if 0
+      // pdf values scaled so that their sum will equal to 1.
+      for(std::size_t point_i = 0; point_i < points.size(); ++point_i) {
+        double probability = probabilities[center_i][point_i] / sum;
+        probability = (CGAL::max)(probability, epsilon);
+        probabilities[center_i][point_i] = -log(probability);
+      }
+#else
+      //pdf values scaled between [0-1]
+      std::pair<std::vector<double>::iterator, std::vector<double>::iterator>
+      min_max_pair =
+        CGAL::min_max_element(probabilities[center_i].begin(),
+                              probabilities[center_i].end());
+      double max_value = *min_max_pair.second, min_value = *min_max_pair.first;
+      double max_min_dif = max_value - min_value;
+      for(std::size_t point_i = 0; point_i < points.size(); ++point_i) {
+        double probability = probabilities[center_i][point_i];
+        probability = (probability - min_value) / max_min_dif;
+        probability = (CGAL::max)(probability, epsilon);
+        probabilities[center_i][point_i] = -log(probability);
+      }
+#endif
+
+    }
+  }
 protected:
 
   // Initialization functions for centers.
@@ -257,7 +298,7 @@ protected:
       likelihood = iterate(iteration_count == 1);
       is_converged = likelihood - prev_likelihood < threshold * fabs(likelihood);
     }
-    SEG_DEBUG(std::cout << likelihood << " " << iteration_count << std::endl)
+    //SEG_DEBUG(std::cout << likelihood << " " << iteration_count << std::endl)
     return likelihood;
   }
 
@@ -276,6 +317,7 @@ protected:
         max_likelihood = likelihood;
       }
     }
+    SEG_DEBUG(std::cout << "max likelihood: " << max_likelihood << std::endl)
     centers = max_centers;
   }
 
diff --git a/Surface_mesh_segmentation/include/CGAL/internal/Surface_mesh_segmentation/K_means_clustering.h b/Surface_mesh_segmentation/include/CGAL/internal/Surface_mesh_segmentation/K_means_clustering.h
index 11c89145407..c7c53ed6e4e 100644
--- a/Surface_mesh_segmentation/include/CGAL/internal/Surface_mesh_segmentation/K_means_clustering.h
+++ b/Surface_mesh_segmentation/include/CGAL/internal/Surface_mesh_segmentation/K_means_clustering.h
@@ -152,7 +152,11 @@ public:
 
       initiate_centers_randomly(number_of_centers);
       calculate_clustering();
+#if 0
       double new_error = sum_of_squares();
+#else
+      double new_error = within_cluster_sum_of_squares();
+#endif
       if(error > new_error) {
         error = new_error;
         min_centers = centers;
@@ -176,6 +180,15 @@ public:
     return sum;
   }
 
+  double within_cluster_sum_of_squares() const {
+    double sum = 0;
+    for(std::vector<K_means_point>::const_iterator point_it = points.begin();
+        point_it != points.end(); ++point_it) {
+      sum += pow(centers[point_it->center_id].mean - point_it->data, 2);
+    }
+    return sum;
+  }
+
   void clear_center_ids() {
     for(std::vector<K_means_point>::iterator point_it = points.begin();
         point_it != points.end(); ++point_it) {