c++ - 如何调整 boost::property_map 以便像 ublas::vector 一样使用它？

Question

我正在寻找一种将 Boost Graph Library 与 Boost uBLAS 结合使用的巧妙方法。更准确地说，我需要使用图邻接矩阵和包含其他一些的 vector 之间的标量积的结果来更新每个顶点的给定顶点属性每个顶点的顶点属性。让我给你一个(不幸的是冗长的)最小的例子来说明这个问题:

#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/iteration_macros.hpp>
#include <boost/numeric/ublas/matrix.hpp>
#include <boost/numeric/ublas/io.hpp>

using namespace boost;
namespace ublas = boost::numeric::ublas;


struct Vertex {             //Using bundled vertex properties

        double old_potential; 
        double new_potential; 
};


typedef adjacency_list< listS, vecS, directedS, Vertex > Graph;

int main(){ 

  //[Prepare a graph with two vertex property maps and initialize
  Graph graph; 
  add_edge (0, 1, graph); 
  add_edge (0, 3, graph); 
  add_edge (1, 2, graph); 

  auto  v_old_potential = boost::get( &Vertex::old_potential, graph );
  auto  v_new_potential = boost::get( &Vertex::new_potential, graph );

  unsigned int source_strength = 0;

  BGL_FORALL_VERTICES( v, graph, Graph )    {

    v_old_potential[v] = source_strength++;
    v_new_potential[v] = 0;
  }
  //]  


  //[ Extracting the adjacency matrix by iteration through all edges --> uBLAS matrix
  ublas::zero_matrix<int> zero_matrix( num_vertices(graph) , num_vertices(graph) ); 
  ublas::matrix<int> adjacency_matrix( zero_matrix );       //initialize properly

  BGL_FORALL_EDGES( e, graph, Graph )   {

     adjacency_matrix( source(e,graph), target(e,graph) ) = 1;
     adjacency_matrix( target(e,graph), source(e,graph) ) = 1;
  }
  //]


  //[ Extracting the old potentials by iteration through all vertices --> uBLAS vector
  ublas::zero_vector<double> zero_vector( num_vertices(graph) );
  ublas::vector<double> old_potential_vector( zero_vector );    //initialize properly
  ublas::vector<double> new_potential_vector( zero_vector );    //initialize properly

  BGL_FORALL_VERTICES(v, graph, Graph)    {

        old_potential_vector( vertex(v,graph) ) = v_old_potential[v];
  }
  //]


  //[ Compute new potentials = A . old potentials ! 
  new_potential_vector = ublas::prod ( adjacency_matrix, old_potential_vector );        //     new = A.old
  //]


  //[ Updating the property map for the new potentials with the newly computed values from above
  BGL_FORALL_VERTICES(v, graph, Graph)    {

        v_new_potential[v] = old_potential_vector( vertex(v,graph) );
  }
  //]

  std::cout << adjacency_matrix << std::endl;       //output = [4,4]((0,1,0,1),(1,0,1,0),(0,1,0,0),(1,0,0,0))
  std::cout << old_potential_vector << std::endl;   //output = [4](0,1,2,3)
  std::cout << new_potential_vector << std::endl;   //output = [4](4,2,1,0)

}

现在，虽然我的建议是一个可能的解决方案，但我对此并不十分满意。问题是，(a) 我将整个 old_potential 属性映射复制到关联的 ublas::vector 以计算标量积。 (b) 我还需要遍历 new_potential 属性映射，以便将新计算的值返回到图中。我怀疑这些操作会在我的应用程序中多次重复，这就是为什么我想从一开始就尽可能干净地完成这部分。

理想情况下，我希望完成所有这些来回复制，而是使用某种适配器 使boost::property_map 作为ublas::vector 在 prod() 的调用中。使用这样的东西会很棒:

adapter(new_potential) = ublas::prod( adjacency_matrix, adapter(old_potential) );

如果有人知道如何实现此类功能或如何改进我的解决方案，我将不胜感激。

Answer 1

#include <iostream>
#include <memory>
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/iteration_macros.hpp>
#include <boost/numeric/ublas/matrix.hpp>
#include <boost/numeric/ublas/io.hpp>

using namespace boost;
namespace ublas = boost::numeric::ublas;

enum vertex_old_potential_t { vertex_old_potential };
enum vertex_new_potential_t { vertex_new_potential };

namespace boost
{
  BOOST_INSTALL_PROPERTY(vertex, new_potential);
  BOOST_INSTALL_PROPERTY(vertex, old_potential);
}

typedef property<vertex_new_potential_t, double, property<vertex_old_potential_t,double> > Vertex;


typedef adjacency_list< listS, vecS, directedS, Vertex > Graph;

struct ublas_vector_map;

namespace boost {
  template<>
  struct property_map< Graph, vertex_new_potential_t > {
    typedef ublas_vector_map type;
    typedef ublas_vector_map const_type;
  };

  template<>
  struct property_map< Graph, vertex_old_potential_t > {
    typedef ublas_vector_map type;
    typedef ublas_vector_map const_type;
  };
}

struct ublas_vector_map : put_get_helper<double&,ublas_vector_map> {
  typedef double value_type;
  typedef value_type& reference;
  typedef typename graph_traits<Graph>::vertex_descriptor key_type;
  typedef boost::lvalue_property_map_tag category;

  ublas_vector_map(Graph* g, vertex_old_potential_t&):vec(new ublas::vector<double>(num_vertices(*g),0.0)){}
  ublas_vector_map(Graph* g, vertex_new_potential_t&):vec(new ublas::vector<double>(num_vertices(*g),0.0)){}


  reference operator[](key_type v) const {
    return (*vec)(v);
  }

  ublas::vector<double>& vector() { return *vec; }

  private:
   std::unique_ptr<ublas::vector<double> > vec;
};

int main(){ 

  //[Prepare a graph with two vertex property maps and initialize
  Graph graph; 
  add_edge (0, 1, graph); 
  add_edge (0, 3, graph); 
  add_edge (1, 2, graph); 

  auto  v_old_potential = boost::get( vertex_old_potential, graph );
  auto  v_new_potential = boost::get( vertex_new_potential, graph );

  unsigned int source_strength = 0;

  BGL_FORALL_VERTICES( v, graph, Graph )    {

    v_old_potential[v] = source_strength++;
  }
  //]  


  //[ Extracting the adjacency matrix by iteration through all edges --> uBLAS matrix
  ublas::zero_matrix<int> zero_matrix( num_vertices(graph) , num_vertices(graph) ); 
  ublas::matrix<int> adjacency_matrix( zero_matrix );       //initialize properly

  BGL_FORALL_EDGES( e, graph, Graph )   {

     adjacency_matrix( source(e,graph), target(e,graph) ) = 1;
     adjacency_matrix( target(e,graph), source(e,graph) ) = 1;
  }
  //]



  //[ Compute new potentials = A . old potentials ! 
  v_new_potential.vector() = ublas::prod ( adjacency_matrix, v_old_potential.vector() );        //     new = A.old
  //]




  std::cout << adjacency_matrix << std::endl;       //output = [4,4]((0,1,0,1),(1,0,1,0),(0,1,0,0),(1,0,0,0))
  std::cout << v_old_potential.vector() << std::endl;   //output = [4](0,1,2,3)
  std::cout << v_new_potential.vector() << std::endl;   //output = [4](4,2,1,0)

  //You must access the properties via v_new_potential and v_old_potential, if you use get... again it resets
  std::cout << v_new_potential[0] << std::endl;
  std::cout << get(vertex_new_potential, graph)[0] << std::endl;

}