I'm studying MST algorithms in GPU recently.I need BGL implementation as coparison,But I have a problem in using prim_minimum_spanning_tree.hpp.The problem is:when I use large input(e.g. >1M),the result is wrong,all the parent of vertices is "no parent".But when the input(e.g. 1K) is small,the result is noproblem. I haven't found know the reason yet.My complier is gcc 4.1.2,OS is RHEL5.

#include <iostream>

#include <boost/graph/adjacency_list.hpp>

#include <boost/graph/prim_minimum_spanning_tree.hpp>

#include <fstream>

#include <string.h>

using namespace std;

int main()

{

using namespace boost;

typedef adjacency_list < vecS, vecS, undirectedS,

property<vertex_distance_t, long>, property < edge_weight_t, int > > Graph;

typedef std::pair < long, long >E;

//read graph data from file

long num_nodes,num_edges,u,v;

int w;

ifstream infile;

infile.open("convertResult.txt");

if(!infile)

{

cerr<<"error:unable to open file."<<endl;

return -1;

}

infile>>num_nodes>>num_edges;

E edges[num_edges];

int weights[num_edges];

for(long i=0;i<num_edges;i++)

{

infile>>u>>v>>w;

edges[i] = make_pair(u,v);

weights[i] = w;

}

//construct input parameters

Graph g(edges, edges + sizeof(edges) / sizeof(E), weights, num_nodes);

property_map<Graph, edge_weight_t>::type weightmap = get(edge_weight, g);

std::vector < graph_traits < Graph >::vertex_descriptor >

p(num_vertices(g));

//call the BGL PRIM

prim_minimum_spanning_tree(g, &p[0]);

//output the result

ofstream outfile;

outfile.open("primResult.txt");

for (std::size_t i = 0; i != p.size(); ++i)

if (p[i] != i)

outfile<< "parent[" << i << "] = " << p[i] << std::endl;

else

outfile<< "parent[" << i << "] = no parent" << std::endl;

return EXIT_SUCCESS;

}