Merge pull request #127 from VincentRouvreau/alpha_complex_with_cgal_epeck_d

Alpha complex with cgal epeck d

13 files changed, 248 insertions, 86 deletions

diff --git a/src/Alpha_complex/doc/Intro_alpha_complex.h b/src/Alpha_complex/doc/Intro_alpha_complex.h
index b075d1fc..adc1378f 100644
--- a/src/Alpha_complex/doc/Intro_alpha_complex.h
+++ b/src/Alpha_complex/doc/Intro_alpha_complex.h
@@ -51,6 +51,17 @@ namespace alpha_complex {
  * - For people only interested in the topology of the \ref alpha_complex (for instance persistence),
  * \ref alpha_complex is equivalent to the \ref cech_complex and much smaller if you do not bound the radii.
  * \ref cech_complex can still make sense in higher dimension precisely because you can bound the radii.
+ * - Using the default `CGAL::Epeck_d` makes the construction safe. If you pass exact=true to create_complex, the
+ * filtration values are the exact ones converted to the filtration value type of the simplicial complex. This can be
+ * very slow. If you pass exact=false (the default), the filtration values are only guaranteed to have a small
+ * multiplicative error compared to the exact value, see <code><a class="el" target="_blank"
+ * href="https://doc.cgal.org/latest/Number_types/classCGAL_1_1Lazy__exact__nt.html">
+ * CGAL::Lazy_exact_nt<NT>::set_relative_precision_of_to_double</a></code> for details. A drawback, when computing
+ * persistence, is that an empty exact interval [10^12,10^12] may become a non-empty approximate interval
+ * [10^12,10^12+10^6]. Using `CGAL::Epick_d` makes the computations slightly faster, and the combinatorics are still
+ * exact, but the computation of filtration values can exceptionally be arbitrarily bad. In all cases, we still
+ * guarantee that the output is a valid filtration (faces have a filtration value no larger than their cofaces).
+ * - For performances reasons, it is advised to use `Alpha_complex` with \ref cgal &ge; 5.0.0.
  *
  * \section pointsexample Example from points
  *
diff --git a/src/Alpha_complex/example/Alpha_complex_from_off.cpp b/src/Alpha_complex/example/Alpha_complex_from_off.cpp
index d411e90a..220a66de 100644
--- a/src/Alpha_complex/example/Alpha_complex_from_off.cpp
+++ b/src/Alpha_complex/example/Alpha_complex_from_off.cpp
@@ -2,8 +2,6 @@
 // to construct a simplex_tree from alpha complex
 #include <gudhi/Simplex_tree.h>
 
-#include <CGAL/Epick_d.h>
-
 #include <iostream>
 #include <string>
 
@@ -23,22 +21,21 @@ int main(int argc, char **argv) {
   // ----------------------------------------------------------------------------
   // Init of an alpha complex from an OFF file
   // ----------------------------------------------------------------------------
-  using Kernel = CGAL::Epick_d< CGAL::Dynamic_dimension_tag >;
-  Gudhi::alpha_complex::Alpha_complex<Kernel> alpha_complex_from_file(off_file_name);
+  Gudhi::alpha_complex::Alpha_complex<> alpha_complex_from_file(off_file_name);
 
-  std::streambuf* streambufffer;
+  std::streambuf* streambuffer;
   std::ofstream ouput_file_stream;
 
   if (argc == 4) {
     ouput_file_stream.open(std::string(argv[3]));
-    streambufffer = ouput_file_stream.rdbuf();
+    streambuffer = ouput_file_stream.rdbuf();
   } else {
-    streambufffer = std::cout.rdbuf();
+    streambuffer = std::cout.rdbuf();
   }
 
   Gudhi::Simplex_tree<> simplex;
   if (alpha_complex_from_file.create_complex(simplex, alpha_square_max_value)) {
-    std::ostream output_stream(streambufffer);
+    std::ostream output_stream(streambuffer);
 
     // ----------------------------------------------------------------------------
     // Display information about the alpha complex
diff --git a/src/Alpha_complex/example/Alpha_complex_from_points.cpp b/src/Alpha_complex/example/Alpha_complex_from_points.cpp
index 981aa470..6526ca3a 100644
--- a/src/Alpha_complex/example/Alpha_complex_from_points.cpp
+++ b/src/Alpha_complex/example/Alpha_complex_from_points.cpp
@@ -2,12 +2,13 @@
 // to construct a simplex_tree from alpha complex
 #include <gudhi/Simplex_tree.h>
 
-#include <CGAL/Epick_d.h>
+#include <CGAL/Epeck_d.h>
 
 #include <iostream>
 #include <vector>
 
-using Kernel = CGAL::Epick_d< CGAL::Dimension_tag<2> >;
+// Explicit dimension 2 Epeck_d kernel
+using Kernel = CGAL::Epeck_d< CGAL::Dimension_tag<2> >;
 using Point = Kernel::Point_d;
 using Vector_of_points = std::vector<Point>;
 
diff --git a/src/Alpha_complex/example/CMakeLists.txt b/src/Alpha_complex/example/CMakeLists.txt
index b069b443..b0337934 100644
--- a/src/Alpha_complex/example/CMakeLists.txt
+++ b/src/Alpha_complex/example/CMakeLists.txt
@@ -5,9 +5,12 @@ if (NOT CGAL_WITH_EIGEN3_VERSION VERSION_LESS 4.11.0)
   target_link_libraries(Alpha_complex_example_from_points  ${CGAL_LIBRARY})
   add_executable ( Alpha_complex_example_from_off Alpha_complex_from_off.cpp )
   target_link_libraries(Alpha_complex_example_from_off ${CGAL_LIBRARY})
+  add_executable ( Alpha_complex_example_fast_from_off Fast_alpha_complex_from_off.cpp )
+  target_link_libraries(Alpha_complex_example_fast_from_off ${CGAL_LIBRARY})
   if (TBB_FOUND)
     target_link_libraries(Alpha_complex_example_from_points ${TBB_LIBRARIES})
     target_link_libraries(Alpha_complex_example_from_off ${TBB_LIBRARIES})
+    target_link_libraries(Alpha_complex_example_fast_from_off ${TBB_LIBRARIES})
   endif()
 
   add_test(NAME Alpha_complex_example_from_points COMMAND $<TARGET_FILE:Alpha_complex_example_from_points>)
@@ -16,7 +19,13 @@ if (NOT CGAL_WITH_EIGEN3_VERSION VERSION_LESS 4.11.0)
       "${CMAKE_SOURCE_DIR}/data/points/alphacomplexdoc.off" "60.0" "${CMAKE_CURRENT_BINARY_DIR}/alphaoffreader_result_60.txt")
   add_test(NAME Alpha_complex_example_from_off_32 COMMAND $<TARGET_FILE:Alpha_complex_example_from_off>
       "${CMAKE_SOURCE_DIR}/data/points/alphacomplexdoc.off" "32.0" "${CMAKE_CURRENT_BINARY_DIR}/alphaoffreader_result_32.txt")
-  if (DIFF_PATH)
+
+  add_test(NAME Alpha_complex_example_fast_from_off_60 COMMAND $<TARGET_FILE:Alpha_complex_example_fast_from_off>
+      "${CMAKE_SOURCE_DIR}/data/points/alphacomplexdoc.off" "60.0" "${CMAKE_CURRENT_BINARY_DIR}/fastalphaoffreader_result_60.txt")
+  add_test(NAME Alpha_complex_example_fast_from_off_32 COMMAND $<TARGET_FILE:Alpha_complex_example_fast_from_off>
+      "${CMAKE_SOURCE_DIR}/data/points/alphacomplexdoc.off" "32.0" "${CMAKE_CURRENT_BINARY_DIR}/fastalphaoffreader_result_32.txt")
+
+if (DIFF_PATH)
     # Do not forget to copy test results files in current binary dir
     file(COPY "alphaoffreader_for_doc_32.txt" DESTINATION ${CMAKE_CURRENT_BINARY_DIR}/)
     file(COPY "alphaoffreader_for_doc_60.txt" DESTINATION ${CMAKE_CURRENT_BINARY_DIR}/)
@@ -25,6 +34,11 @@ if (NOT CGAL_WITH_EIGEN3_VERSION VERSION_LESS 4.11.0)
         ${CMAKE_CURRENT_BINARY_DIR}/alphaoffreader_result_60.txt ${CMAKE_CURRENT_BINARY_DIR}/alphaoffreader_for_doc_60.txt)
     add_test(Alpha_complex_example_from_off_32_diff_files ${DIFF_PATH}
         ${CMAKE_CURRENT_BINARY_DIR}/alphaoffreader_result_32.txt ${CMAKE_CURRENT_BINARY_DIR}/alphaoffreader_for_doc_32.txt)
+
+    add_test(Alpha_complex_example_fast_from_off_60_diff_files ${DIFF_PATH}
+        ${CMAKE_CURRENT_BINARY_DIR}/fastalphaoffreader_result_60.txt ${CMAKE_CURRENT_BINARY_DIR}/alphaoffreader_for_doc_60.txt)
+    add_test(Alpha_complex_example_fast_from_off_32_diff_files ${DIFF_PATH}
+        ${CMAKE_CURRENT_BINARY_DIR}/fastalphaoffreader_result_32.txt ${CMAKE_CURRENT_BINARY_DIR}/alphaoffreader_for_doc_32.txt)
   endif()
 
   add_executable ( Alpha_complex_example_weighted_3d_from_points Weighted_alpha_complex_3d_from_points.cpp )
diff --git a/src/Alpha_complex/example/Fast_alpha_complex_from_off.cpp b/src/Alpha_complex/example/Fast_alpha_complex_from_off.cpp
new file mode 100644
index 00000000..f181005a
--- /dev/null
+++ b/src/Alpha_complex/example/Fast_alpha_complex_from_off.cpp
@@ -0,0 +1,65 @@
+#include <gudhi/Alpha_complex.h>
+// to construct a simplex_tree from alpha complex
+#include <gudhi/Simplex_tree.h>
+
+#include <CGAL/Epick_d.h>
+
+#include <iostream>
+#include <string>
+
+void usage(int nbArgs, char * const progName) {
+  std::cerr << "Error: Number of arguments (" << nbArgs << ") is not correct\n";
+  std::cerr << "Usage: " << progName << " filename.off alpha_square_max_value [ouput_file.txt]\n";
+  std::cerr << "       i.e.: " << progName << " ../../data/points/alphacomplexdoc.off 60.0\n";
+  exit(-1);  // ----- >>
+}
+
+int main(int argc, char **argv) {
+  if ((argc != 3) && (argc != 4)) usage(argc, (argv[0] - 1));
+
+  std::string off_file_name {argv[1]};
+  double alpha_square_max_value {atof(argv[2])};
+
+  // WARNING : CGAL::Epick_d is fast but not safe (unlike CGAL::Epeck_d)
+  // (i.e. when the points are on a grid)
+  using Fast_kernel = CGAL::Epick_d<CGAL::Dynamic_dimension_tag>;
+  // ----------------------------------------------------------------------------
+  // Init of an alpha complex from an OFF file
+  // ----------------------------------------------------------------------------
+  Gudhi::alpha_complex::Alpha_complex<Fast_kernel> alpha_complex_from_file(off_file_name);
+
+  std::streambuf* streambuffer;
+  std::ofstream ouput_file_stream;
+
+  if (argc == 4) {
+    ouput_file_stream.open(std::string(argv[3]));
+    streambuffer = ouput_file_stream.rdbuf();
+  } else {
+    streambuffer = std::cout.rdbuf();
+  }
+
+  Gudhi::Simplex_tree<> simplex;
+  if (alpha_complex_from_file.create_complex(simplex, alpha_square_max_value)) {
+    std::ostream output_stream(streambuffer);
+
+    // ----------------------------------------------------------------------------
+    // Display information about the alpha complex
+    // ----------------------------------------------------------------------------
+    output_stream << "Alpha complex is of dimension " << simplex.dimension() <<
+        " - " << simplex.num_simplices() << " simplices - " <<
+        simplex.num_vertices() << " vertices." << std::endl;
+
+    output_stream << "Iterator on alpha complex simplices in the filtration order, with [filtration value]:" <<
+        std::endl;
+    for (auto f_simplex : simplex.filtration_simplex_range()) {
+      output_stream << "   ( ";
+      for (auto vertex : simplex.simplex_vertex_range(f_simplex)) {
+        output_stream << vertex << " ";
+      }
+      output_stream << ") -> " << "[" << simplex.filtration(f_simplex) << "] ";
+      output_stream << std::endl;
+    }
+  }
+  ouput_file_stream.close();
+  return 0;
+}
diff --git a/src/Alpha_complex/include/gudhi/Alpha_complex.h b/src/Alpha_complex/include/gudhi/Alpha_complex.h
index 8919cdb9..0c2569c8 100644
--- a/src/Alpha_complex/include/gudhi/Alpha_complex.h
+++ b/src/Alpha_complex/include/gudhi/Alpha_complex.h
@@ -20,11 +20,12 @@
 #include <math.h>  // isnan, fmax
 
 #include <CGAL/Delaunay_triangulation.h>
-#include <CGAL/Epick_d.h>
+#include <CGAL/Epeck_d.h>  // For EXACT or SAFE version
+#include <CGAL/Epick_d.h>  // For FAST version
 #include <CGAL/Spatial_sort_traits_adapter_d.h>
 #include <CGAL/property_map.h>  // for CGAL::Identity_property_map
-#include <CGAL/NT_converter.h>
 #include <CGAL/version.h>  // for CGAL_VERSION_NR
+#include <CGAL/NT_converter.h>
 
 #include <Eigen/src/Core/util/Macros.h>  // for EIGEN_VERSION_AT_LEAST
 
@@ -39,17 +40,20 @@
 
 // Make compilation fail - required for external projects - https://github.com/GUDHI/gudhi-devel/issues/10
 #if CGAL_VERSION_NR < 1041101000
-# error Alpha_complex_3d is only available for CGAL >= 4.11
+# error Alpha_complex is only available for CGAL >= 4.11
 #endif
 
 #if !EIGEN_VERSION_AT_LEAST(3,1,0)
-# error Alpha_complex_3d is only available for Eigen3 >= 3.1.0 installed with CGAL
+# error Alpha_complex is only available for Eigen3 >= 3.1.0 installed with CGAL
 #endif
 
 namespace Gudhi {
 
 namespace alpha_complex {
 
+template<typename D> struct Is_Epeck_D { static const bool value = false; };
+template<typename D> struct Is_Epeck_D<CGAL::Epeck_d<D>> { static const bool value = true; };
+
 /**
  * \class Alpha_complex Alpha_complex.h gudhi/Alpha_complex.h
  * \brief Alpha complex data structure.
@@ -63,17 +67,31 @@ namespace alpha_complex {
  * 
  * Please refer to \ref alpha_complex for examples.
  *
- * The complex is a template class requiring an Epick_d <a target="_blank"
+ * The complex is a template class requiring an <a target="_blank"
+ * href="https://doc.cgal.org/latest/Kernel_d/structCGAL_1_1Epeck__d.html">CGAL::Epeck_d</a>,
+ * or an <a target="_blank"
+ * href="https://doc.cgal.org/latest/Kernel_d/structCGAL_1_1Epick__d.html">CGAL::Epick_d</a> <a target="_blank"
  * href="http://doc.cgal.org/latest/Kernel_d/index.html#Chapter_dD_Geometry_Kernel">dD Geometry Kernel</a>
  * \cite cgal:s-gkd-15b from CGAL as template, default value is <a target="_blank"
- * href="http://doc.cgal.org/latest/Kernel_d/classCGAL_1_1Epick__d.html">CGAL::Epick_d</a>
+ * href="https://doc.cgal.org/latest/Kernel_d/structCGAL_1_1Epeck__d.html">CGAL::Epeck_d</a>
  * < <a target="_blank" href="http://doc.cgal.org/latest/Kernel_23/classCGAL_1_1Dynamic__dimension__tag.html">
  * CGAL::Dynamic_dimension_tag </a> >
  * 
- * \remark When Alpha_complex is constructed with an infinite value of alpha, the complex is a Delaunay complex.
- * 
+ * \remark
+ * - When Alpha_complex is constructed with an infinite value of alpha, the complex is a Delaunay complex.
+ * - Using the default `CGAL::Epeck_d` makes the construction safe. If you pass exact=true to create_complex, the
+ * filtration values are the exact ones converted to the filtration value type of the simplicial complex. This can be
+ * very slow. If you pass exact=false (the default), the filtration values are only guaranteed to have a small
+ * multiplicative error compared to the exact value, see <code><a class="el" target="_blank"
+ * href="https://doc.cgal.org/latest/Number_types/classCGAL_1_1Lazy__exact__nt.html">
+ * CGAL::Lazy_exact_nt<NT>::set_relative_precision_of_to_double</a></code> for details. A drawback, when computing
+ * persistence, is that an empty exact interval [10^12,10^12] may become a non-empty approximate interval
+ * [10^12,10^12+10^6]. Using `CGAL::Epick_d` makes the computations slightly faster, and the combinatorics are still
+ * exact, but the computation of filtration values can exceptionally be arbitrarily bad. In all cases, we still
+ * guarantee that the output is a valid filtration (faces have a filtration value no larger than their cofaces).
+ * - For performances reasons, it is advised to use `Alpha_complex` with \ref cgal &ge; 5.0.0.
  */
-template<class Kernel = CGAL::Epick_d<CGAL::Dynamic_dimension_tag>>
+template<class Kernel = CGAL::Epeck_d<CGAL::Dynamic_dimension_tag>>
 class Alpha_complex {
  public:
   // Add an int in TDS to save point index in the structure
@@ -184,6 +202,12 @@ class Alpha_complex {
  private:
   template<typename InputPointRange >
   void init_from_range(const InputPointRange& points) {
+    #if CGAL_VERSION_NR < 1050000000
+    if (Is_Epeck_D<Kernel>::value)
+      std::cerr << "It is strongly advised to use a CGAL version >= 5.0 with Epeck_d Kernel for performance reasons."
+                << std::endl;
+    #endif
+
     auto first = std::begin(points);
     auto last = std::end(points);
 
@@ -237,6 +261,8 @@ class Alpha_complex {
    * @param[in] complex SimplicialComplexForAlpha to be created.
    * @param[in] max_alpha_square maximum for alpha square value. Default value is +\f$\infty\f$, and there is very
    * little point using anything else since it does not save time.
+   * @param[in] exact Exact filtration values computation. Not exact if `Kernel` is not <a target="_blank"
+   * href="https://doc.cgal.org/latest/Kernel_d/structCGAL_1_1Epeck__d.html">CGAL::Epeck_d</a>.
    * 
    * @return true if creation succeeds, false otherwise.
    * 
@@ -248,7 +274,8 @@ class Alpha_complex {
   template <typename SimplicialComplexForAlpha,
             typename Filtration_value = typename SimplicialComplexForAlpha::Filtration_value>
   bool create_complex(SimplicialComplexForAlpha& complex,
-                      Filtration_value max_alpha_square = std::numeric_limits<Filtration_value>::infinity()) {
+                      Filtration_value max_alpha_square = std::numeric_limits<Filtration_value>::infinity(),
+                      bool exact = false) {
     // From SimplicialComplexForAlpha type required to insert into a simplicial complex (with or without subfaces).
     typedef typename SimplicialComplexForAlpha::Vertex_handle Vertex_handle;
     typedef typename SimplicialComplexForAlpha::Simplex_handle Simplex_handle;
@@ -324,9 +351,13 @@ class Alpha_complex {
             if (f_simplex_dim > 0) {
               // squared_radius function initialization
               Squared_Radius squared_radius = kernel_.compute_squared_radius_d_object();
-              CGAL::NT_converter<typename Geom_traits::FT, Filtration_value> cv;
 
-              alpha_complex_filtration = cv(squared_radius(pointVector.begin(), pointVector.end()));
+              CGAL::NT_converter<typename Geom_traits::FT, Filtration_value> cv;
+              auto sqrad = squared_radius(pointVector.begin(), pointVector.end());
+#if CGAL_VERSION_NR >= 1050000000
+              if(exact) CGAL::exact(sqrad);
+#endif
+              alpha_complex_filtration = cv(sqrad);
             }
             complex.assign_filtration(f_simplex, alpha_complex_filtration);
 #ifdef DEBUG_TRACES
diff --git a/src/Alpha_complex/test/Alpha_complex_unit_test.cpp b/src/Alpha_complex/test/Alpha_complex_unit_test.cpp
index 01e4cee3..40b3fe09 100644
--- a/src/Alpha_complex/test/Alpha_complex_unit_test.cpp
+++ b/src/Alpha_complex/test/Alpha_complex_unit_test.cpp
@@ -15,6 +15,7 @@
 
 #include <CGAL/Delaunay_triangulation.h>
 #include <CGAL/Epick_d.h>
+#include <CGAL/Epeck_d.h>
 
 #include <cmath>  // float comparison
 #include <limits>
@@ -28,12 +29,16 @@
 #include <gudhi/Unitary_tests_utils.h>
 
 // Use dynamic_dimension_tag for the user to be able to set dimension
-typedef CGAL::Epick_d< CGAL::Dynamic_dimension_tag > Kernel_d;
+typedef CGAL::Epeck_d< CGAL::Dynamic_dimension_tag > Exact_kernel_d;
 // Use static dimension_tag for the user not to be able to set dimension
-typedef CGAL::Epick_d< CGAL::Dimension_tag<3> > Kernel_s;
+typedef CGAL::Epeck_d< CGAL::Dimension_tag<3> > Exact_kernel_s;
+// Use dynamic_dimension_tag for the user to be able to set dimension
+typedef CGAL::Epick_d< CGAL::Dynamic_dimension_tag > Inexact_kernel_d;
+// Use static dimension_tag for the user not to be able to set dimension
+typedef CGAL::Epick_d< CGAL::Dimension_tag<3> > Inexact_kernel_s;
 // The triangulation uses the default instantiation of the TriangulationDataStructure template parameter
 
-typedef boost::mpl::list<Kernel_d, Kernel_s> list_of_kernel_variants;
+typedef boost::mpl::list<Exact_kernel_d, Exact_kernel_s, Inexact_kernel_d, Inexact_kernel_s> list_of_kernel_variants;
 
 BOOST_AUTO_TEST_CASE_TEMPLATE(Alpha_complex_from_OFF_file, TestedKernel, list_of_kernel_variants) {
   // ----------------------------------------------------------------------------
@@ -86,7 +91,7 @@ BOOST_AUTO_TEST_CASE_TEMPLATE(Alpha_complex_from_OFF_file, TestedKernel, list_of
 }
 
 // Use static dimension_tag for the user not to be able to set dimension
-typedef CGAL::Epick_d< CGAL::Dimension_tag<4> > Kernel_4;
+typedef CGAL::Epeck_d< CGAL::Dimension_tag<4> > Kernel_4;
 typedef Kernel_4::Point_d Point_4;
 typedef std::vector<Point_4> Vector_4_Points;
 
diff --git a/src/Alpha_complex/utilities/CMakeLists.txt b/src/Alpha_complex/utilities/CMakeLists.txt
index 5295f3cd..57b92942 100644
--- a/src/Alpha_complex/utilities/CMakeLists.txt
+++ b/src/Alpha_complex/utilities/CMakeLists.txt
@@ -7,9 +7,19 @@ if (NOT CGAL_WITH_EIGEN3_VERSION VERSION_LESS 4.11.0)
   if (TBB_FOUND)
     target_link_libraries(alpha_complex_persistence ${TBB_LIBRARIES})
   endif(TBB_FOUND)
-  add_test(NAME Alpha_complex_utilities_alpha_complex_persistence COMMAND $<TARGET_FILE:alpha_complex_persistence>
-      "${CMAKE_SOURCE_DIR}/data/points/tore3D_300.off" "-p" "2" "-m" "0.45")
-
+  add_test(NAME Alpha_complex_utilities_safe_alpha_complex_persistence COMMAND $<TARGET_FILE:alpha_complex_persistence>
+      "${CMAKE_SOURCE_DIR}/data/points/tore3D_300.off" "-p" "2" "-m" "0.45" "-o" "safe.pers")
+  add_test(NAME Alpha_complex_utilities_fast_alpha_complex_persistence COMMAND $<TARGET_FILE:alpha_complex_persistence>
+      "${CMAKE_SOURCE_DIR}/data/points/tore3D_300.off" "-p" "2" "-m" "0.45" "-o" "fast.pers" "-f")
+  add_test(NAME Alpha_complex_utilities_exact_alpha_complex_persistence COMMAND $<TARGET_FILE:alpha_complex_persistence>
+      "${CMAKE_SOURCE_DIR}/data/points/tore3D_300.off" "-p" "2" "-m" "0.45" "-o" "exact.pers" "-e")
+  if (DIFF_PATH)
+    add_test(Alpha_complex_utilities_diff_exact_alpha_complex ${DIFF_PATH}
+             "exact.pers" "safe.pers")
+    add_test(Alpha_complex_utilities_diff_fast_alpha_complex ${DIFF_PATH}
+             "fast.pers" "safe.pers")
+  endif()
+  
   install(TARGETS alpha_complex_persistence DESTINATION bin)
 
   add_executable(alpha_complex_3d_persistence alpha_complex_3d_persistence.cpp)
@@ -20,21 +30,21 @@ if (NOT CGAL_WITH_EIGEN3_VERSION VERSION_LESS 4.11.0)
 
   add_test(NAME Alpha_complex_utilities_alpha_complex_3d COMMAND $<TARGET_FILE:alpha_complex_3d_persistence>
           "${CMAKE_SOURCE_DIR}/data/points/tore3D_300.off"
-          "-p" "2" "-m" "0.45" "-o" "safe.pers")
+          "-p" "2" "-m" "0.45" "-o" "safe_3d.pers")
 
   add_test(NAME Alpha_complex_utilities_exact_alpha_complex_3d COMMAND $<TARGET_FILE:alpha_complex_3d_persistence>
           "${CMAKE_SOURCE_DIR}/data/points/tore3D_300.off"
-          "-p" "2" "-m" "0.45" "-o" "exact.pers" "-e")
+          "-p" "2" "-m" "0.45" "-o" "exact_3d.pers" "-e")
 
   add_test(NAME Alpha_complex_utilities_safe_alpha_complex_3d COMMAND $<TARGET_FILE:alpha_complex_3d_persistence>
           "${CMAKE_SOURCE_DIR}/data/points/tore3D_300.off"
-          "-p" "2" "-m" "0.45" "-o" "fast.pers" "-f")
+          "-p" "2" "-m" "0.45" "-o" "fast_3d.pers" "-f")
 
   if (DIFF_PATH)
-    add_test(Alpha_complex_utilities_diff_alpha_complex_3d ${DIFF_PATH}
-            "exact.pers" "safe.pers")
-    add_test(Alpha_complex_utilities_diff_alpha_complex_3d ${DIFF_PATH}
-            "fast.pers" "safe.pers")
+    add_test(Alpha_complex_utilities_diff_exact_alpha_complex_3d ${DIFF_PATH}
+            "exact_3d.pers" "safe_3d.pers")
+    add_test(Alpha_complex_utilities_diff_fast_alpha_complex_3d ${DIFF_PATH}
+            "fast_3d.pers" "safe_3d.pers")
   endif()
 
   add_test(NAME Alpha_complex_utilities_periodic_alpha_complex_3d_persistence COMMAND $<TARGET_FILE:alpha_complex_3d_persistence>
diff --git a/src/Alpha_complex/utilities/alpha_complex_persistence.cpp b/src/Alpha_complex/utilities/alpha_complex_persistence.cpp
index fab7bd30..486347cc 100644
--- a/src/Alpha_complex/utilities/alpha_complex_persistence.cpp
+++ b/src/Alpha_complex/utilities/alpha_complex_persistence.cpp
@@ -24,63 +24,84 @@
 using Simplex_tree = Gudhi::Simplex_tree<>;
 using Filtration_value = Simplex_tree::Filtration_value;
 
-void program_options(int argc, char *argv[], std::string &off_file_points, std::string &output_file_diag,
-                     Filtration_value &alpha_square_max_value, int &coeff_field_characteristic,
-                     Filtration_value &min_persistence);
+void program_options(int argc, char *argv[], std::string &off_file_points, bool &exact, bool &fast,
+                     std::string &output_file_diag, Filtration_value &alpha_square_max_value,
+                     int &coeff_field_characteristic, Filtration_value &min_persistence);
 
 int main(int argc, char **argv) {
   std::string off_file_points;
   std::string output_file_diag;
+  bool exact_version = false;
+  bool fast_version = false;
   Filtration_value alpha_square_max_value;
   int coeff_field_characteristic;
   Filtration_value min_persistence;
 
-  program_options(argc, argv, off_file_points, output_file_diag, alpha_square_max_value, coeff_field_characteristic,
-                  min_persistence);
+  program_options(argc, argv, off_file_points, exact_version, fast_version, output_file_diag, alpha_square_max_value,
+                  coeff_field_characteristic, min_persistence);
 
-  // ----------------------------------------------------------------------------
-  // Init of an alpha complex from an OFF file
-  // ----------------------------------------------------------------------------
-  using Kernel = CGAL::Epick_d<CGAL::Dynamic_dimension_tag>;
-  Gudhi::alpha_complex::Alpha_complex<Kernel> alpha_complex_from_file(off_file_points);
+  if ((exact_version) && (fast_version)) {
+    std::cerr << "You cannot set the exact and the fast version." << std::endl;
+    exit(-1);
+  }
 
   Simplex_tree simplex;
-  if (alpha_complex_from_file.create_complex(simplex, alpha_square_max_value)) {
-    // ----------------------------------------------------------------------------
-    // Display information about the alpha complex
-    // ----------------------------------------------------------------------------
-    std::cout << "Simplicial complex is of dimension " << simplex.dimension() << " - " << simplex.num_simplices()
-              << " simplices - " << simplex.num_vertices() << " vertices." << std::endl;
-
-    // Sort the simplices in the order of the filtration
-    simplex.initialize_filtration();
-
-    std::cout << "Simplex_tree dim: " << simplex.dimension() << std::endl;
-    // Compute the persistence diagram of the complex
-    Gudhi::persistent_cohomology::Persistent_cohomology<Simplex_tree, Gudhi::persistent_cohomology::Field_Zp> pcoh(
-        simplex);
-    // initializes the coefficient field for homology
-    pcoh.init_coefficients(coeff_field_characteristic);
-
-    pcoh.compute_persistent_cohomology(min_persistence);
-
-    // Output the diagram in filediag
-    if (output_file_diag.empty()) {
-      pcoh.output_diagram();
-    } else {
-      std::cout << "Result in file: " << output_file_diag << std::endl;
-      std::ofstream out(output_file_diag);
-      pcoh.output_diagram(out);
-      out.close();
+  if (fast_version) {
+    // WARNING : CGAL::Epick_d is fast but not safe (unlike CGAL::Epeck_d)
+    // (i.e. when the points are on a grid)
+    using Fast_kernel = CGAL::Epick_d<CGAL::Dynamic_dimension_tag>;
+
+    // Init of an alpha complex from an OFF file
+    Gudhi::alpha_complex::Alpha_complex<Fast_kernel> alpha_complex_from_file(off_file_points);
+
+    if (!alpha_complex_from_file.create_complex(simplex, alpha_square_max_value)) {
+      std::cerr << "Fast Alpha complex simplicial complex creation failed." << std::endl;
+      exit(-1);
     }
-  }
+  } else {
+    using Kernel = CGAL::Epeck_d<CGAL::Dynamic_dimension_tag>;
 
+    // Init of an alpha complex from an OFF file
+    Gudhi::alpha_complex::Alpha_complex<Kernel> alpha_complex_from_file(off_file_points);
+
+    if (!alpha_complex_from_file.create_complex(simplex, alpha_square_max_value, exact_version)) {
+      std::cerr << "Alpha complex simplicial complex creation failed." << std::endl;
+      exit(-1);
+    }
+  }
+  // ----------------------------------------------------------------------------
+  // Display information about the alpha complex
+  // ----------------------------------------------------------------------------
+  std::cout << "Simplicial complex is of dimension " << simplex.dimension() << " - " << simplex.num_simplices()
+            << " simplices - " << simplex.num_vertices() << " vertices." << std::endl;
+
+  // Sort the simplices in the order of the filtration
+  simplex.initialize_filtration();
+
+  std::cout << "Simplex_tree dim: " << simplex.dimension() << std::endl;
+  // Compute the persistence diagram of the complex
+  Gudhi::persistent_cohomology::Persistent_cohomology<Simplex_tree, Gudhi::persistent_cohomology::Field_Zp> pcoh(
+      simplex);
+  // initializes the coefficient field for homology
+  pcoh.init_coefficients(coeff_field_characteristic);
+
+  pcoh.compute_persistent_cohomology(min_persistence);
+
+  // Output the diagram in filediag
+  if (output_file_diag.empty()) {
+    pcoh.output_diagram();
+  } else {
+    std::cout << "Result in file: " << output_file_diag << std::endl;
+    std::ofstream out(output_file_diag);
+    pcoh.output_diagram(out);
+    out.close();
+  }
   return 0;
 }
 
-void program_options(int argc, char *argv[], std::string &off_file_points, std::string &output_file_diag,
-                     Filtration_value &alpha_square_max_value, int &coeff_field_characteristic,
-                     Filtration_value &min_persistence) {
+void program_options(int argc, char *argv[], std::string &off_file_points, bool &exact, bool &fast,
+                     std::string &output_file_diag, Filtration_value &alpha_square_max_value,
+                     int &coeff_field_characteristic, Filtration_value &min_persistence) {
   namespace po = boost::program_options;
   po::options_description hidden("Hidden options");
   hidden.add_options()("input-file", po::value<std::string>(&off_file_points),
@@ -88,6 +109,10 @@ void program_options(int argc, char *argv[], std::string &off_file_points, std::
 
   po::options_description visible("Allowed options", 100);
   visible.add_options()("help,h", "produce help message")(
+      "exact,e", po::bool_switch(&exact),
+      "To activate exact version of Alpha complex (default is false, not available if fast is set)")(
+      "fast,f", po::bool_switch(&fast),
+      "To activate fast version of Alpha complex (default is false, not available if exact is set)")(
       "output-file,o", po::value<std::string>(&output_file_diag)->default_value(std::string()),
       "Name of file in which the persistence diagram is written. Default print in std::cout")(
       "max-alpha-square-value,r", po::value<Filtration_value>(&alpha_square_max_value)
diff --git a/src/Alpha_complex/utilities/alphacomplex.md b/src/Alpha_complex/utilities/alphacomplex.md
index fcd16a3b..527598a9 100644
--- a/src/Alpha_complex/utilities/alphacomplex.md
+++ b/src/Alpha_complex/utilities/alphacomplex.md
@@ -46,6 +46,8 @@ for the Alpha complex construction.
 coefficient field Z/pZ for computing homology.

 * `-m [ --min-persistence ]` (default = 0) Minimal lifetime of homology feature

 to be recorded. Enter a negative value to see zero length intervals.

+* `-e [ --exact ]` for the exact computation version.

+* `-f [ --fast ]` for the fast computation version.

 

 **Example**

 

diff --git a/src/Rips_complex/example/example_rips_complex_from_csv_distance_matrix_file.cpp b/src/Rips_complex/example/example_rips_complex_from_csv_distance_matrix_file.cpp
index 9e182f1e..b7040453 100644
--- a/src/Rips_complex/example/example_rips_complex_from_csv_distance_matrix_file.cpp
+++ b/src/Rips_complex/example/example_rips_complex_from_csv_distance_matrix_file.cpp
@@ -35,19 +35,19 @@ int main(int argc, char **argv) {
   Distance_matrix distances = Gudhi::read_lower_triangular_matrix_from_csv_file<Filtration_value>(csv_file_name);
   Rips_complex rips_complex_from_file(distances, threshold);
 
-  std::streambuf* streambufffer;
+  std::streambuf* streambuffer;
   std::ofstream ouput_file_stream;
 
   if (argc == 5) {
     ouput_file_stream.open(std::string(argv[4]));
-    streambufffer = ouput_file_stream.rdbuf();
+    streambuffer = ouput_file_stream.rdbuf();
   } else {
-    streambufffer = std::cout.rdbuf();
+    streambuffer = std::cout.rdbuf();
   }
 
   Simplex_tree stree;
   rips_complex_from_file.create_complex(stree, dim_max);
-  std::ostream output_stream(streambufffer);
+  std::ostream output_stream(streambuffer);
 
   // ----------------------------------------------------------------------------
   // Display information about the Rips complex
diff --git a/src/Rips_complex/example/example_rips_complex_from_off_file.cpp b/src/Rips_complex/example/example_rips_complex_from_off_file.cpp
index de2e4ea4..36b468a7 100644
--- a/src/Rips_complex/example/example_rips_complex_from_off_file.cpp
+++ b/src/Rips_complex/example/example_rips_complex_from_off_file.cpp
@@ -34,19 +34,19 @@ int main(int argc, char **argv) {
   Gudhi::Points_off_reader<Point> off_reader(off_file_name);
   Rips_complex rips_complex_from_file(off_reader.get_point_cloud(), threshold, Gudhi::Euclidean_distance());
 
-  std::streambuf* streambufffer;
+  std::streambuf* streambuffer;
   std::ofstream ouput_file_stream;
 
   if (argc == 5) {
     ouput_file_stream.open(std::string(argv[4]));
-    streambufffer = ouput_file_stream.rdbuf();
+    streambuffer = ouput_file_stream.rdbuf();
   } else {
-    streambufffer = std::cout.rdbuf();
+    streambuffer = std::cout.rdbuf();
   }
 
   Simplex_tree stree;
   rips_complex_from_file.create_complex(stree, dim_max);
-  std::ostream output_stream(streambufffer);
+  std::ostream output_stream(streambuffer);
 
   // ----------------------------------------------------------------------------
   // Display information about the Rips complex
diff --git a/src/common/doc/main_page.md b/src/common/doc/main_page.md
index d8cbf97f..e8d11fdf 100644
--- a/src/common/doc/main_page.md
+++ b/src/common/doc/main_page.md
@@ -45,6 +45,7 @@
     values of the codimension 1 cofaces that make it not Gabriel otherwise.
     All simplices that have a filtration value strictly greater than a given alpha squared value are not inserted into
     the complex.<br>
+    For performances reasons, it is advised to use \ref cgal &ge; 5.0.0.
     </td>
     <td width="15%">
       <b>Author:</b> Vincent Rouvreau<br>