3 files changed, 188 insertions, 0 deletions
diff --git a/utilities/Cech_complex/CMakeLists.txt b/utilities/Cech_complex/CMakeLists.txt
new file mode 100644
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+++ b/utilities/Cech_complex/CMakeLists.txt
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+cmake_minimum_required(VERSION 2.6)
+project(Cech_complex_utilities)
+
+add_executable(cech_persistence cech_persistence.cpp)
+target_link_libraries(cech_persistence ${Boost_PROGRAM_OPTIONS_LIBRARY})
+
+if (TBB_FOUND)
+  target_link_libraries(cech_persistence ${TBB_LIBRARIES})
+endif()
+
+add_test(NAME Cech_complex_utility_from_rips_on_tore_3D COMMAND $<TARGET_FILE:cech_persistence>
+    "${CMAKE_SOURCE_DIR}/data/points/tore3D_300.off" "-r" "0.25" "-m" "0.5" "-d" "3" "-p" "3")
+
+install(TARGETS cech_persistence DESTINATION bin)
diff --git a/utilities/Cech_complex/cech_persistence.cpp b/utilities/Cech_complex/cech_persistence.cpp
new file mode 100644
index 00000000..abd9dbcd
--- /dev/null
+++ b/utilities/Cech_complex/cech_persistence.cpp
@@ -0,0 +1,136 @@
+/*    This file is part of the Gudhi Library. The Gudhi library
+ *    (Geometric Understanding in Higher Dimensions) is a generic C++
+ *    library for computational topology.
+ *
+ *    Author(s):       Vincent Rouvreau
+ *
+ *    Copyright (C) 2018 Inria
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the GNU General Public License as published by
+ *    the Free Software Foundation, either version 3 of the License, or
+ *    (at your option) any later version.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU General Public License for more details.
+ *
+ *    You should have received a copy of the GNU General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <gudhi/Cech_complex.h>
+#include <gudhi/distance_functions.h>
+#include <gudhi/Simplex_tree.h>
+#include <gudhi/Persistent_cohomology.h>
+#include <gudhi/Points_off_io.h>
+
+#include <boost/program_options.hpp>
+
+#include <string>
+#include <vector>
+#include <limits>  // infinity
+
+// Types definition
+using Simplex_tree = Gudhi::Simplex_tree<Gudhi::Simplex_tree_options_fast_persistence>;
+using Filtration_value = Simplex_tree::Filtration_value;
+using Point = std::vector<double>;
+using Point_cloud = std::vector<Point>;
+using Points_off_reader = Gudhi::Points_off_reader<Point>;
+using Cech_complex = Gudhi::cech_complex::Cech_complex<Simplex_tree, Point_cloud>;
+using Field_Zp = Gudhi::persistent_cohomology::Field_Zp;
+using Persistent_cohomology = Gudhi::persistent_cohomology::Persistent_cohomology<Simplex_tree, Field_Zp>;
+
+void program_options(int argc, char* argv[], std::string& off_file_points, std::string& filediag,
+                     Filtration_value& max_radius, int& dim_max, int& p, Filtration_value& min_persistence);
+
+int main(int argc, char* argv[]) {
+  std::string off_file_points;
+  std::string filediag;
+  Filtration_value max_radius;
+  int dim_max;
+  int p;
+  Filtration_value min_persistence;
+
+  program_options(argc, argv, off_file_points, filediag, max_radius, dim_max, p, min_persistence);
+
+  Points_off_reader off_reader(off_file_points);
+  Cech_complex cech_complex_from_file(off_reader.get_point_cloud(), max_radius);
+
+  // Construct the Cech complex in a Simplex Tree
+  Simplex_tree simplex_tree;
+
+  cech_complex_from_file.create_complex(simplex_tree, dim_max);
+  std::cout << "The complex contains " << simplex_tree.num_simplices() << " simplices \n";
+  std::cout << "   and has dimension " << simplex_tree.dimension() << " \n";
+
+  // Sort the simplices in the order of the filtration
+  simplex_tree.initialize_filtration();
+
+  // Compute the persistence diagram of the complex
+  Persistent_cohomology pcoh(simplex_tree);
+  // initializes the coefficient field for homology
+  pcoh.init_coefficients(p);
+
+  pcoh.compute_persistent_cohomology(min_persistence);
+
+  // Output the diagram in filediag
+  if (filediag.empty()) {
+    pcoh.output_diagram();
+  } else {
+    std::ofstream out(filediag);
+    pcoh.output_diagram(out);
+    out.close();
+  }
+
+  return 0;
+}
+
+void program_options(int argc, char* argv[], std::string& off_file_points, std::string& filediag,
+                     Filtration_value& max_radius, int& dim_max, int& p, 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),
+                       "Name of an OFF file containing a point set.\n");
+
+  po::options_description visible("Allowed options", 100);
+  visible.add_options()("help,h", "produce help message")(
+      "output-file,o", po::value<std::string>(&filediag)->default_value(std::string()),
+      "Name of file in which the persistence diagram is written. Default print in std::cout")(
+      "max-radius,r",
+      po::value<Filtration_value>(&max_radius)->default_value(std::numeric_limits<Filtration_value>::infinity()),
+      "Maximal length of an edge for the Cech complex construction.")(
+      "cpx-dimension,d", po::value<int>(&dim_max)->default_value(1),
+      "Maximal dimension of the Cech complex we want to compute.")(
+      "field-charac,p", po::value<int>(&p)->default_value(11),
+      "Characteristic p of the coefficient field Z/pZ for computing homology.")(
+      "min-persistence,m", po::value<Filtration_value>(&min_persistence),
+      "Minimal lifetime of homology feature to be recorded. Default is 0. Enter a negative value to see zero length "
+      "intervals");
+
+  po::positional_options_description pos;
+  pos.add("input-file", 1);
+
+  po::options_description all;
+  all.add(visible).add(hidden);
+
+  po::variables_map vm;
+  po::store(po::command_line_parser(argc, argv).options(all).positional(pos).run(), vm);
+  po::notify(vm);
+
+  if (vm.count("help") || !vm.count("input-file")) {
+    std::cout << std::endl;
+    std::cout << "Compute the persistent homology with coefficient field Z/pZ \n";
+    std::cout << "of a Cech complex defined on a set of input points.\n \n";
+    std::cout << "The output diagram contains one bar per line, written with the convention: \n";
+    std::cout << "   p   dim b d \n";
+    std::cout << "where dim is the dimension of the homological feature,\n";
+    std::cout << "b and d are respectively the birth and death of the feature and \n";
+    std::cout << "p is the characteristic of the field Z/pZ used for homology coefficients." << std::endl << std::endl;
+
+    std::cout << "Usage: " << argv[0] << " [options] input-file" << std::endl << std::endl;
+    std::cout << visible << std::endl;
+    std::abort();
+  }
+}
diff --git a/utilities/Cech_complex/cechcomplex.md b/utilities/Cech_complex/cechcomplex.md
new file mode 100644
index 00000000..f7817dbb
--- /dev/null
+++ b/utilities/Cech_complex/cechcomplex.md
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+
+
+# Čech complex #
+
+## cech_persistence ##
+This program computes the persistent homology with coefficient field *Z/pZ* of
+a Čech complex defined on a set of input points, using Euclidean distance. The
+output diagram contains one bar per line, written with the convention:
+
+`p dim birth death`
+
+where `dim` is the dimension of the homological feature, `birth` and `death`
+are respectively the birth and death of the feature, and `p` is the
+characteristic of the field *Z/pZ* used for homology coefficients (`p` must be
+a prime number).
+
+**Usage**
+
+`cech_persistence [options] <OFF input file>`
+
+**Allowed options**
+
+* `-h [ --help ]` Produce help message
+* `-o [ --output-file ]` Name of file in which the persistence diagram is written. Default print in standard output.
+* `-r [ --max-edge-length ]` (default = inf) Maximal length of an edge for the Čech complex construction.
+* `-d [ --cpx-dimension ]` (default = 1) Maximal dimension of the Čech complex we want to compute.
+* `-p [ --field-charac ]` (default = 11) Characteristic p of the 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.
+
+Beware: this program may use a lot of RAM and take a lot of time if `max-edge-length` is set to a large value.
+
+**Example 1 with Z/2Z coefficients**
+
+`cech_persistence ../../data/points/tore3D_1307.off -r 0.25 -m 0.5 -d 3 -p 2`
+
+**Example 2 with Z/3Z coefficients**
+
+`cech_persistence ../../data/points/tore3D_1307.off -r 0.25 -m 0.5 -d 3 -p 3`