graph_simplicial_complex.h

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/*    This file is part of the Gudhi Library - https://gudhi.inria.fr/ - which is released under MIT.
 *    See file LICENSE or go to https://gudhi.inria.fr/licensing/ for full license details.
 *    Author(s):       Clément Maria
 *
 *    Copyright (C) 2014 Inria
 *
 *    Modification(s):
 *      - YYYY/MM Author: Description of the modification
 */

#ifndef GRAPH_SIMPLICIAL_COMPLEX_H_
#define GRAPH_SIMPLICIAL_COMPLEX_H_

#include <boost/graph/adjacency_list.hpp>

#include <utility>  // for pair<>
#include <vector>
#include <map>
#include <tuple>  // for std::tie

namespace Gudhi {
/* Edge tag for Boost PropertyGraph. */
struct edge_filtration_t {
  typedef boost::edge_property_tag kind;
};

/* Vertex tag for Boost PropertyGraph. */
struct vertex_filtration_t {
  typedef boost::vertex_property_tag kind;
};

template <typename SimplicialComplexForProximityGraph>
using Proximity_graph = typename boost::adjacency_list < boost::vecS, boost::vecS, boost::directedS
, boost::property < vertex_filtration_t, typename SimplicialComplexForProximityGraph::Filtration_value >
, boost::property < edge_filtration_t, typename SimplicialComplexForProximityGraph::Filtration_value >>;

template< typename SimplicialComplexForProximityGraph
          , typename ForwardPointRange
          , typename Distance >
Proximity_graph<SimplicialComplexForProximityGraph> compute_proximity_graph(
    const ForwardPointRange& points,
    typename SimplicialComplexForProximityGraph::Filtration_value threshold,
    Distance distance) {
  using Vertex_handle = typename SimplicialComplexForProximityGraph::Vertex_handle;
  using Filtration_value = typename SimplicialComplexForProximityGraph::Filtration_value;

  std::vector<std::pair< Vertex_handle, Vertex_handle >> edges;
  std::vector< Filtration_value > edges_fil;
  std::map< Vertex_handle, Filtration_value > vertices;

  Vertex_handle idx_u, idx_v;
  Filtration_value fil;
  idx_u = 0;
  for (auto it_u = points.begin(); it_u != points.end(); ++it_u) {
    idx_v = idx_u + 1;
    for (auto it_v = it_u + 1; it_v != points.end(); ++it_v, ++idx_v) {
      fil = distance(*it_u, *it_v);
      if (fil <= threshold) {
        edges.emplace_back(idx_u, idx_v);
        edges_fil.push_back(fil);
      }
    }
    ++idx_u;
  }

  // Points are labeled from 0 to idx_u-1
  Proximity_graph<SimplicialComplexForProximityGraph> skel_graph(edges.begin(), edges.end(), edges_fil.begin(), idx_u);

  auto vertex_prop = boost::get(vertex_filtration_t(), skel_graph);

  typename boost::graph_traits<Proximity_graph<SimplicialComplexForProximityGraph>>::vertex_iterator vi, vi_end;
  for (std::tie(vi, vi_end) = boost::vertices(skel_graph);
       vi != vi_end; ++vi) {
    boost::put(vertex_prop, *vi, 0.);
  }

  return skel_graph;
}

}  // namespace Gudhi

#endif  // GRAPH_SIMPLICIAL_COMPLEX_H_