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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/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 <vector>
#include <cstddef>
#include <iterator> // for std::size
namespace Gudhi {
namespace cech_complex {
/**
* \class Cech_complex
* \brief Cech complex data structure.
*
* \ingroup Cech_complex
*
* \details
* The data structure is a one skeleton graph, or Rips graph, containing edges when the edge length is less or equal
* to a given threshold. Edge length is computed from a user given point cloud with a given distance function, or a
* distance matrix.
*
* \tparam Filtration_value is the type used to store the filtration values of the simplicial complex.
*/
template<typename SimplicialComplexForCechComplex, typename ForwardPointRange>
class Cech_complex {
private:
using Vertex_handle = typename SimplicialComplexForCechComplex::Vertex_handle;
using Filtration_value = typename SimplicialComplexForCechComplex::Filtration_value;
using Proximity_graph = Gudhi::Proximity_graph<SimplicialComplexForCechComplex>;
public:
/** \brief Cech_complex constructor from a list of points.
*
* @param[in] points Range of points.
* @param[in] threshold Rips value.
* @param[in] distance distance function that returns a `Filtration_value` from 2 given points.
*
* \tparam ForwardPointRange must be a range for which `std::begin` and `std::end` return input iterators on a
* point.
*
* \tparam Distance furnishes `operator()(const Point& p1, const Point& p2)`, where
* `Point` is a point from the `ForwardPointRange`, and that returns a `Filtration_value`.
*/
template<typename Distance >
Cech_complex(const ForwardPointRange& points, Filtration_value threshold, Distance distance)
: threshold_(threshold),
point_cloud_(points) {
GUDHI_CHECK(std::size(points) > 0,
std::invalid_argument("Cech_complex::create_complex - point cloud is empty"));
dimension_ = points[0].size();
cech_skeleton_graph_ = Gudhi::compute_proximity_graph<SimplicialComplexForCechComplex>(point_cloud_, threshold_, distance);
}
/** \brief Initializes the simplicial complex from the Rips graph and expands it until a given maximal
* dimension.
*
* @param[in] complex SimplicialComplexForCech to be created.
* @param[in] dim_max graph expansion for Rips until this given maximal dimension.
* @exception std::invalid_argument In debug mode, if `complex.num_vertices()` does not return 0.
*
*/
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, ForwardPointRange>(complex, this));
}
Filtration_value threshold() const {
return threshold_;
}
std::size_t dimension() const {
return dimension_;
}
auto point(std::size_t vertex) const -> decltype(point_cloud_.begin() + vertex) {
GUDHI_CHECK((point_cloud_.begin() + vertex) < point_cloud_.end(),
std::invalid_argument("Cech_complex::point - simplicial complex is not empty"));
return (point_cloud_.begin() + vertex);
}
private:
Proximity_graph cech_skeleton_graph_;
Filtration_value threshold_;
ForwardPointRange point_cloud_;
std::size_t dimension_;
};
} // namespace cech_complex
} // namespace Gudhi
#endif // CECH_COMPLEX_H_
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