/* 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): Marc Glisse
*
* 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 .
*/
#ifndef SPARSE_RIPS_COMPLEX_H_
#define SPARSE_RIPS_COMPLEX_H_
#include
#include
#include
#include
#include
#include
namespace Gudhi {
namespace rips_complex {
// The whole interface is copied on Rips_complex. A redesign should be discussed with all complex creation classes in mind.
/**
* \class Sparse_rips_complex
* \brief Sparse Rips complex data structure.
*
* \ingroup rips_complex
*
* \details
* This class is used to construct a sparse \f$(1+\epsilon)\f$-approximation of `Rips_complex`, i.e. a filtered simplicial complex that is multiplicatively \f$(1+\epsilon)\f$-interleaved with the Rips filtration.
*
* \tparam Filtration_value is the type used to store the filtration values of the simplicial complex.
*/
template
class Sparse_rips_complex {
private:
// TODO: use a different graph where we know we can safely insert in parallel.
typedef typename boost::adjacency_list
, boost::property> Graph;
typedef int Vertex_handle;
public:
/** \brief Sparse_rips_complex constructor from a list of points.
*
* @param[in] points Range of points.
* @param[in] distance distance function that returns a `Filtration_value` from 2 given points.
* @param[in] epsilon (1+epsilon) is the desired approximation factor. epsilon must be positive.
*
*/
template
Sparse_rips_complex(const RandomAccessPointRange& points, Distance distance, double epsilon) {
GUDHI_CHECK(epsilon > 0, "epsilon must be positive");
std::vector sorted_points;
std::vector params;
auto dist_fun = [&](Vertex_handle i, Vertex_handle j){return distance(points[i], points[j]);};
Ker kernel(dist_fun);
subsampling::choose_n_farthest_points(kernel, boost::irange(0, boost::size(points)), -1, -1, std::back_inserter(sorted_points), std::back_inserter(params));
compute_sparse_graph(sorted_points, params, dist_fun, epsilon);
}
/** \brief Rips_complex constructor from a distance matrix.
*
* @param[in] distance_matrix Range of range of distances.
* `distance_matrix[i][j]` returns the distance between points \f$i\f$ and
* \f$j\f$ as long as \f$ 0 \leqslant i < j \leqslant
* distance\_matrix.size().\f$
* @param[in] epsilon (1+epsilon) is the desired approximation factor. epsilon must be positive.
*/
template
Sparse_rips_complex(const DistanceMatrix& distance_matrix, double epsilon)
: Sparse_rips_complex(
boost::irange(0, boost::size(distance_matrix)),
[&](Vertex_handle i, Vertex_handle j){return distance_matrix[j][i];},
epsilon) {}
/** \brief Fills the simplicial complex with the sparse Rips graph and
* expands it with all the cliques, stopping at a given maximal dimension.
*
* \tparam SimplicialComplexForRips must meet `SimplicialComplexForRips` concept.
*
* @param[in] complex the complex to fill
* @param[in] dim_max maximal dimension of the simplicial complex.
* @exception std::invalid_argument In debug mode, if `complex.num_vertices()` does not return 0.
*
*/
template
void create_complex(SimplicialComplexForRips& complex, int dim_max) {
GUDHI_CHECK(complex.num_vertices() == 0,
std::invalid_argument("Sparse_rips_complex::create_complex - simplicial complex is not empty"));
complex.insert_graph(graph_);
complex.expansion(dim_max);
}
private:
// choose_n_farthest_points wants the distance function in this form...
template
struct Ker {
typedef std::size_t Point_d; // index into point range
Ker(Distance& d) : dist (d) {}
// Despite the name, this is not squared...
typedef Distance Squared_distance_d;
Squared_distance_d& squared_distance_d_object() const { return dist; }
Distance& dist;
};
// PointRange must be random access.
template
void compute_sparse_graph(const PointRange& points, const ParamRange& params, Distance& dist, double epsilon) {
const int n = boost::size(points);
graph_.~Graph();
new(&graph_) Graph(n);
//for(auto v : vertices(g)) // doesn't work :-(
typename boost::graph_traits::vertex_iterator v_i, v_e;
for(std::tie(v_i, v_e) = vertices(graph_); v_i != v_e; ++v_i) {
auto v = *v_i;
// This whole loop might not be necessary, leave it until someone investigates if it is safe to remove.
put(vertex_filtration_t(), graph_, v, 0);
}
// TODO:
// - make it parallel
// - only test near-enough neighbors
for(int i = 0; i < n; ++i)
for(int j = i + 1; j < n; ++j){
auto&& pi = points[i];
auto&& pj = points[j];
auto d = dist(pi, pj);
auto li = params[i];
auto lj = params[j];
GUDHI_CHECK(lj <= li, "Bad furthest point sorting");
Filtration_value alpha;
// The paper has d/2 and d-lj/e to match the Cech, but we use doubles to match the Rips
if(d * epsilon <= 2 * lj)
alpha = d;
else if(d * epsilon <= li + lj && (epsilon >= 1 || d * epsilon <= lj * (1 + 1 / (1 - epsilon))))
alpha = (d - lj / epsilon) * 2;
else continue;
add_edge(pi, pj, alpha, graph_);
}
}
Graph graph_;
};
} // namespace rips_complex
} // namespace Gudhi
#endif // SPARSE_RIPS_COMPLEX_H_