graph_simplicial_complex.h

 /*    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):       Clément Maria
  *
  *    Copyright (C) 2014  INRIA Sophia Antipolis-Méditerranée (France)
  *
  *    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 GUDHI_GRAPH_SIMPLICIAL_COMPLEX_FILTRATION_TAG_H
#define GUDHI_GRAPH_SIMPLICIAL_COMPLEX_FILTRATION_TAG_H

#include <boost/graph/adjacency_list.hpp>

/* 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;
};

typedef int                                       Vertex_handle;
typedef double                                    Filtration_value;
typedef boost::adjacency_list < boost::vecS, boost::vecS, boost::undirectedS
                              , boost::property < vertex_filtration_t, Filtration_value >
                              , boost::property < edge_filtration_t, Filtration_value > 
                              >                   Graph_t;
typedef std::pair< Vertex_handle, Vertex_handle > Edge_t;

template< typename PointCloud
        , typename Point >
Graph_t compute_proximity_graph( PointCloud &points
                               , Filtration_value threshold 
                               , Filtration_value distance(Point p1, Point p2) )
{
  std::vector< Edge_t >                       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;
  }

  Graph_t skel_graph( edges.begin()
                    , edges.end()
                    , edges_fil.begin()
                    , idx_u); //number of points labeled from 0 to idx_u-1

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

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

#endif // GUDHI_GRAPH_SIMPLICIAL_COMPLEX_FILTRATION_TAG_H