我正在寻找一种智能方法，将 Boost图库与 Boost uBLAS 结合使用。更确切地说，我需要使用图形邻接矩阵之间的标量积的结果和包含其他的向量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lenghty）最小的例子来说明问题：
#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，以便计算标量积。并且（b）我还需要遍历new_potential属性映射以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重复很多，这就是为什么我希望从一开始就让这部分尽可能干净。
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来使boost::property_map作为ublas::vector工作prod()的号召。使用这样的东西真是太棒了：
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，我将非常感激。
答案 0 :(得分：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;
}