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+/* 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/>.
+ */
+
+#ifndef CECH_COMPLEX_H_
+#define CECH_COMPLEX_H_
+
+#include <gudhi/distance_functions.h> // for Gudhi::Minimal_enclosing_ball_radius
+#include <gudhi/graph_simplicial_complex.h> // for Gudhi::Proximity_graph
+#include <gudhi/Debug_utils.h> // for GUDHI_CHECK
+#include <gudhi/Cech_complex_blocker.h> // for Gudhi::cech_complex::Cech_blocker
+
+#include <iostream>
+#include <stdexcept> // for exception management
+#include <vector>
+
+namespace Gudhi {
+
+namespace cech_complex {
+
+/**
+ * \class Cech_complex
+ * \brief Cech complex data structure.
+ *
+ * \ingroup cech_complex
+ *
+ * \details
+ * The data structure is a proximity graph, containing edges when the edge length is less or equal
+ * to a given max_radius. Edge length is computed from `Gudhi::Minimal_enclosing_ball_radius` distance function.
+ *
+ * \tparam SimplicialComplexForProximityGraph furnishes `Vertex_handle` and `Filtration_value` type definition required
+ * by `Gudhi::Proximity_graph`.
+ *
+ * \tparam ForwardPointRange must be a range for which `std::begin()` and `std::end()` methods return input
+ * iterators on a point. `std::begin()` and `std::end()` methods are also required for a point.
+ */
+template <typename SimplicialComplexForProximityGraph, typename ForwardPointRange>
+class Cech_complex {
+ private:
+ // Required by compute_proximity_graph
+ using Vertex_handle = typename SimplicialComplexForProximityGraph::Vertex_handle;
+ using Filtration_value = typename SimplicialComplexForProximityGraph::Filtration_value;
+ using Proximity_graph = Gudhi::Proximity_graph<SimplicialComplexForProximityGraph>;
+
+ // Retrieve Coordinate type from ForwardPointRange
+ using Point_from_range_iterator = typename boost::range_const_iterator<ForwardPointRange>::type;
+ using Point_from_range = typename std::iterator_traits<Point_from_range_iterator>::value_type;
+ using Coordinate_iterator = typename boost::range_const_iterator<Point_from_range>::type;
+ using Coordinate = typename std::iterator_traits<Coordinate_iterator>::value_type;
+
+ public:
+ // Point and Point_cloud type definition
+ using Point = std::vector<Coordinate>;
+ using Point_cloud = std::vector<Point>;
+
+ public:
+ /** \brief Cech_complex constructor from a list of points.
+ *
+ * @param[in] points Range of points.
+ * @param[in] max_radius Maximal radius value.
+ *
+ * \tparam ForwardPointRange must be a range of Point. Point must be a range of <b>copyable</b> Cartesian coordinates.
+ *
+ */
+ Cech_complex(const ForwardPointRange& points, Filtration_value max_radius) : max_radius_(max_radius) {
+ // Point cloud deep copy
+ point_cloud_.reserve(boost::size(points));
+ for (auto&& point : points) point_cloud_.emplace_back(std::begin(point), std::end(point));
+
+ cech_skeleton_graph_ = Gudhi::compute_proximity_graph<SimplicialComplexForProximityGraph>(
+ point_cloud_, max_radius_, Gudhi::Minimal_enclosing_ball_radius());
+ }
+
+ /** \brief Initializes the simplicial complex from the proximity graph and expands it until a given maximal
+ * dimension, using the Cech blocker oracle.
+ *
+ * @param[in] complex SimplicialComplexForCech to be created.
+ * @param[in] dim_max graph expansion until this given maximal dimension.
+ * @exception std::invalid_argument In debug mode, if `complex.num_vertices()` does not return 0.
+ *
+ */
+ template <typename SimplicialComplexForCechComplex>
+ void create_complex(SimplicialComplexForCechComplex& complex, int dim_max) {
+ GUDHI_CHECK(complex.num_vertices() == 0,
+ std::invalid_argument("Cech_complex::create_complex - simplicial complex is not empty"));
+
+ // insert the proximity graph in the simplicial complex
+ complex.insert_graph(cech_skeleton_graph_);
+ // expand the graph until dimension dim_max
+ complex.expansion_with_blockers(dim_max,
+ Cech_blocker<SimplicialComplexForCechComplex, Cech_complex>(&complex, this));
+ }
+
+ /** @return max_radius value given at construction. */
+ Filtration_value max_radius() const { return max_radius_; }
+
+ /** @param[in] vertex Point position in the range.
+ * @return The point.
+ */
+ const Point& get_point(Vertex_handle vertex) const { return point_cloud_[vertex]; }
+
+ private:
+ Proximity_graph cech_skeleton_graph_;
+ Filtration_value max_radius_;
+ Point_cloud point_cloud_;
+};
+
+} // namespace cech_complex
+
+} // namespace Gudhi
+
+#endif // CECH_COMPLEX_H_