我有一个增强图,每个边都有多个权重(想象一天中每小时一组权重).这些权重值中的每一个都存储在propretyEdge类中：
class propretyEdge {
std::map<std::string,double> weights; // Date indexed
}
我创建了一个包含这些属性的图形,然后用正确的值填充它.
现在的问题是我想在图上的特定权重集上启动Dijkstra算法：例如,一个函数可能是：
void Dijkstra (string date,parameters ... )
那将使用
weights[date]
图的每个边的值.
我一遍又一遍地阅读文档,我无法清楚地知道自己要做什么.我当然需要写这样的东西,但我不知道要开始：
boost::dijkstra_shortest_paths (
(*graph_m),vertex_origin_num_l,// weight_map (get (edge_weight,(*graph_m)))
// predecessor_map(boost::make_iterator_property_map(predecessors.begin(),get(boost::vertex_index,(*graph_m)))).
// distance_map(boost::make_iterator_property_map(distances.begin (),get(vertex_index,(*graph_m) )))
predecessor_map(predecessorMap).
distance_map(distanceMap)
);
谢谢您的帮助.
编辑
多亏了精彩的Answer of Sehe,我能够在MacOS和Ubuntu上做到我想要的.
但是当我们尝试在Visual Studio 2012上编译这段代码时,似乎VS并不是很擅长理解boost的指针功能.所以我们修改了Sehe的部分：
auto dated_weight_f = [&](Graph::edge_descriptor ed) {
return g[ed].weights.at(date);
};
auto dated_weight_map = make_function_property_map<Graph::edge_descriptor,double>(dated_weight_f);
通过：
class dated_weight_f {
public:
dated_weight_f(Graph* graph_p,std::string date_p){
graph_m=graph_p;
date_m=date_p;
}
typedef double result_type;
result_type operator()(Edge edge_p) const{
return (*graph_m)[edge_p].weights.at(date_m);
}
private:
Graph* graph_m;
std::string date_m;
};
const auto dated_weight_map = make_function_property_map<Edge>(dated_weight_f(graph_m,date_l));
其中有不使用指针功能的优点.
解决方法
由于显然不清楚这个问题
is answered in the other answer,我会解释.
你真正需要的是一个自定义的weight_map参数,它是“有状态的”,可以为给定的日期选择一个特定的值.
你可以把它变得像你想要的那样复杂¹,所以你甚至可以在给定未知日期²的情况下插入/推断一个重量,但是为了这个演示的目的,让它保持简单.
让我们如上定义图表类型(大致)：
struct propretyEdge {
std::map<std::string,double> weights; // Date indexed
};
using Graph = adjacency_list<vecS,vecS,directedS,no_property,propretyEdge>;
现在,让我们生成一个随机图,其中包含3个不同日期的随机权重：
int main() {
Graph g;
std::mt19937 prng { std::random_device{}() };
generate_random_graph(g,8,12,prng);
uniform_real<double> weight_dist(10,42);
for (auto e : make_iterator_range(edges(g)))
for (auto&& date : { "2014-01-01","2014-02-01","2014-03-01" })
g[e].weights[date] = weight_dist(prng);
并且,跳到目标：
for (std::string const& date : { "2014-01-01","2014-03-01" }) {
Dijkstra(date,g,0);
}
}
现在你如何实现Dijkstra(…)？从文档示例中收集,你会做类似的事情
void Dijkstra(std::string const& date,Graph const& g,int vertex_origin_num_l = 0) {
// magic postponed ...
std::vector<Graph::vertex_descriptor> p(num_vertices(g));
std::vector<double> d(num_vertices(g));
std::vector<default_color_type> color_map(num_vertices(g));
boost::typed_identity_property_map<Graph::vertex_descriptor> vid; // T* property maps were deprecated
dijkstra_shortest_paths(g,weight_map(dated_weight_map).
predecessor_map(make_iterator_property_map(p.data(),vid)).
distance_map(make_iterator_property_map(d.data(),vid)).
color_map(make_iterator_property_map(color_map.data(),vid))
);
现在唯一不明确的位应该是dated_weight_map.
输入Boost Property Maps
正如我在链接的Is it possible to have several edge weight property maps for one graph BOOST?中所示,您可以拥有各种属性映射³,包括调用用户定义的函数.这是缺失的部分：
auto dated_weight_f = [&](Graph::edge_descriptor ed) {
return g[ed].weights.at(date);
};
auto dated_weight_map = make_function_property_map<Graph::edge_descriptor,double>(dated_weight_f);
Voilà：完成了
我希望到现在为止,问题中的对应关系以及相关问题的答案是清楚的.剩下要做的就是将完整的实时样本和结果发布在漂亮的图片中：
Live On Coliru
#include <boost/property_map/property_map.hpp>
#include <boost/property_map/function_property_map.hpp>
#include <boost/property_map/property_map_iterator.hpp>
#include <random>
#include <boost/graph/random.hpp>
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/dijkstra_shortest_paths.hpp>
#include <fstream>
using namespace boost;
struct propretyEdge {
std::map<std::string,propretyEdge>;
void Dijkstra(std::string const& date,int vertex_origin_num_l = 0) {
auto dated_weight_f = [&](Graph::edge_descriptor ed) {
return g[ed].weights.at(date);
};
auto dated_weight_map = make_function_property_map<Graph::edge_descriptor,double>(dated_weight_f);
std::vector<Graph::vertex_descriptor> p(num_vertices(g));
std::vector<double> d(num_vertices(g));
std::vector<default_color_type> color_map(num_vertices(g));
boost::typed_identity_property_map<Graph::vertex_descriptor> vid; // T* property maps were deprecated
dijkstra_shortest_paths(g,vid))
);
std::cout << "distances and parents for '" + date + "':" << std::endl;
for (auto vd : make_iterator_range(vertices(g)))
{
std::cout << "distance(" << vd << ") = " << d[vd] << ",";
std::cout << "parent(" << vd << ") = " << p[vd] << std::endl;
}
std::cout << std::endl;
std::ofstream dot_file("dijkstra-eg-" + date + ".dot");
dot_file << "digraph D {\n"
" rankdir=LR\n"
" size=\"6,4\"\n"
" ratio=\"fill\"\n"
" graph[label=\"shortest path on " + date + "\"];\n"
" edge[style=\"bold\"]\n"
" node[shape=\"circle\"]\n";
for (auto ed : make_iterator_range(edges(g))) {
auto u = source(ed,g),v = target(ed,g);
dot_file
<< u << " -> " << v << "[label=\"" << get(dated_weight_map,ed) << "\""
<< (p[v] == u?",color=\"black\"" : ",color=\"grey\"")
<< "]";
}
dot_file << "}";
}
int main() {
Graph g;
std::mt19937 prng { std::random_device{}() };
generate_random_graph(g,"2014-03-01" })
g[e].weights[date] = weight_dist(prng);
for (std::string const& date : { "2014-01-01",0);
}
}
输出,例如
¹只要保留您正在调用的算法所需的不变量即可.特别是,在给定相同边缘的情况下,必须在执行期间始终如一地返回相同的权重.此外,一些算法不支持负权重等.
²我强烈建议在这种情况下使用Boost ICL interval_map但我离题了
³另见map set/get requests into C++ class/structure changes